ALBERT

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): Hiral D. Shah, J.A. Bhalodia〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this communication, we report the structural and electrical transport properties of (1-〈em〉x〈/em〉) La〈sub〉0.7〈/sub〉Sr〈sub〉0.3〈/sub〉Mn〈sub〉0.95〈/sub〉Co〈sub〉0.05〈/sub〉O〈sub〉3〈/sub〉 (LSMCO) + (〈em〉x〈/em〉) ZnO (〈em〉x〈/em〉 = 0%, 6%, 9%, 12%, 15% & 18%) composites. For the preparation of (1-〈em〉x〈/em〉) LSMCO + (〈em〉x〈/em〉) ZnO (〈em〉x〈/em〉 = 6%, 9%, 12%, 15% & 18%) composites, sample of LSMCO was prepared by the auto combustion technique/inexpensive modified sol-gel technique. The results of Rietveld refined XRD data show that LSMCO sample possesses a rhombohedral structure with the 〈em〉R-3c〈/em〉 space group whereas ZnO compound remains with hexagonal structure with the 〈em〉P6〈/em〉〈sub〉〈em〉3〈/em〉〈/sub〉〈em〉mc〈/em〉 space group in all the composite samples. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that no any extra unwanted phase was observed in each composite excluding the LSMCO and ZnO phases. ZnO is mostly distributed at the grain boundaries and on the surface of the LSMCO grains. Elemental presence and ratio was confirmed through the EDX analysis. The electrical resistivity of LSMCO and each composite was measured in the temperature range of 2 K–320 K at 0 Oe, 10 kOe, 50 kOe & 90 kOe magnetic field. The results indicate that the ZnO addition increases the resistivity of all the composites compare to that of pure LSMCO. The electrical resistivity explored by the theoretical model below 〈em〉T〈/em〉〈sub〉MI〈/sub〉 and fitting enlightenment for the observed behavior is transmitted here in detail.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): Dezhi Yang, Weihua Liu, Dingfu Cheng, Jieshi Chen, Hao Lu, Chun Yu, Jijin Xu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉(Co, Cr)23C6 type carbide is a typical metallic compound in many cobalt bearing alloys, and it acts as the strengthening phase in the form of bulk eutectic carbides or precipitated carbides. In this work, first-principles calculations were carried out to investigate the electronic structure, phase stability, mechanical and magnetic properties of (Co, Cr)23C6 with different cobalt occupation. Some of the calculated values are compared with previous studies and, they are found to be in a good agreement. The method considering curvature radius is firstly used to describe the degree of anisotropy. The hardness calculated through elastic constants presents an approximate downtrend with the cobalt concentration. Analysis of the density of states (DOS), overlapped population and electron density maps, indicates that the bonds in (Co, Cr)23C6 are the mixture of covalent, ionic and metallic bonds, the interactions of 〈em〉d-d〈/em〉 orbits between metallic atoms contribute most to the hybridization mode. According to the population analysis, the reduction in hardness can attribute to the increase of metallicity and iconicity of the interacted metallic atoms. In addition, the formation of a large quantity of antibonding also plays a negative role in intrinsic hardness of (Co, Cr)23C6 when massive substitution of cobalt atom.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): Morteza Alizadeh, Andisheh Shakery, Erfan Salahinejad〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this research, the structure and mechanical properties of 1050 aluminum strips reinforced with E-glass fibers, processed by the cross accumulative roll bonding (CARB) process, were investigated from microscopic, hardness, tensile and peeling viewpoints. The results indicated that the incorporation of the glass fibers in the Al matrix increases strength and micro-hardness but decreases elongation. In addition, it was realized that some of these fibers are broken and changed to short fibers during the CARB process. The presence of the glass fibers strongly also reduces the bond efficiency of the Al strips, typically from 50% to 5%. To compensate this deleterious effect, it was found that at least 25% should be increased to the normal thickness reduction used in CRAB.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 9 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica〈/p〉 〈p〉Author(s): Bing Xiong, Xiao-qiang Fan, Yi Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉To improve the performance of a hypersonic inward turning inlet, an optimization design method was proposed. A parameterization methodology was developed for an axisymmetric basic flowfield, and the geometry of a basic flowfield can be easily generated in several parameters. Preliminarily, an optimization targeting on the basic flowfield performance was conducted. As a result, the total pressure recovery of the basic flowfield was improved 7.65% compared with the referred one under the same constraints. The corresponding stream-traced inlet performance was also improved 5.65%. For further optimization, an optimization directly targeting on the 3-D inlet performance was carried out. The method of calculating along streamlines (MCS), which is for the fast calculation of a stream-traced inlet flowfield, was proposed and confirmed before this optimization. The result shows that the 3-D inlet total pressure can be further enhanced 6.74% than the previous one, and it is 12.78% higher than the referred one. That is to say, it is more reasonable to target on the inlet performance directly for an optimization, rather than targeting on the basic flowfield performance. By statistically analyzing the optimization data, it was found that the opinion “A better basic flowfield means a better stream-traced inlet” is statistically correct, but not exactly correct. The steam-traced inlet performance is not exactly determined by a basic flowfield, and it is determined by a combination of all the flow tubes the inlet captures.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): J.Y. Oh, Tien M. Le, A.T. Pham, D.H. Tran, D.S. Yang, B. Kang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this work, we investigated a correlation between superconductivity and interlayer coupling of two different alkaline (Na and K)-substituted Bi〈sub〉1·6〈/sub〉Pb〈sub〉0·4〈/sub〉Sr〈sub〉2〈/sub〉Ca〈sub〉2〈/sub〉Cu〈sub〉3〈/sub〉O〈sub〉10+δ〈/sub〉 (BSCCO) polycrystalline samples. The excess conductivity analysis by the Aslamazov-Larkin (AL) and Lawrence-Doniach (LD) theories showed that Na substitution at the Ca site induced a gradual broadening of 3D fluctuation region with increasing interlayer coupling strength, which explains a systematic increase of 〈em〉T〈/em〉〈sub〉〈em〉c〈/em〉〈/sub〉 and a decrease of normal state resistivity. On the other hand, exactly the opposite results were observed in the K-substituted samples in place of Sr. Extended x-ray absorption fine structure (EXAFS) studies revealed that substitution of Na and K generated completely different effects on the local structure around Cu atoms. It is noticeable that the Cu–O bond distance was found to decrease monotonically with the varying amounts of Na, which indicates that the CuO〈sub〉2〈/sub〉 layer is stabilized. On the while, the opposite was observed to occur with the varying amounts of K. Unlike the Cu–Ca bond which was the least affected by the substitution, the Cu–Sr bond distance increased drastically with K substitution. All these findings indicate that Na substitution at the Ca site enhances superconductivity with no loss of interlayer interaction, while K substitution at the Sr site weakens superconductivity due to the diminished interlayer interaction.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): Moara M. Castro, Shima Sabbaghianrad, Pedro Henrique R. Pereira, Eric M. Mazzer, Augusta Isaac, Terence G. Langdon, Roberto B. Figueiredo〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A magnesium/aluminium composite was produced by room temperature consolidation through high-pressure torsion (HPT) processing. Half-discs of the pure metals were placed side-by-side and subjected to different numbers of turns. The initially reduced interface between the phases gradually increased with increasing rotation. The composite displayed a significant ductility even after 10 turns. The distribution of hardness in the HPT-processed discs was bi-modal in the early stages of processing. As the number of turns increased and the thickness of the phases decreased there was a noticeable increase in hardness. The hardness values of the composite further increased after thermal treatment due to the formation of intermetallics within the interface between the magnesium and aluminium-rich phases.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): Lipeng Xu, Fei Zhou, Jizhou Kong, Haobin Zhou, Qian Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The effects of testing temperature on the electrochemical properties of Li(Ni〈sub〉0.6〈/sub〉Mn〈sub〉0.2〈/sub〉Co〈sub〉0.2〈/sub〉)O〈sub〉2〈/sub〉 are investigated in detail. When the testing temperature is 40 °C, the Li(Ni〈sub〉0.6〈/sub〉Mn〈sub〉0.2〈/sub〉Co〈sub〉0.2〈/sub〉)O〈sub〉2〈/sub〉 cathode material possesses the highest initial discharge capacity of 162.4 mAh·g〈sup〉−1〈/sup〉 at 0.5C rate, but their cycling stability decreases markedly. When the test temperature rises up to 60 °C, the side reaction between electrolyte and cathode material becomes serious, and the Li(Ni〈sub〉0.6〈/sub〉Mn〈sub〉0.2〈/sub〉Co〈sub〉0.2〈/sub〉)O〈sub〉2〈/sub〉 cannot work. When the testing temperature decreases, the electrochemical impedances like R〈sub〉ct〈/sub〉 values increase, and then the discharge capacity at 0 °C, −10 °C and −20 °C is only 80%, 53% and 23% of that at 25 °C. Based on the electrochemical impedance spectra at different temperatures, four kinds of equivalent circuit models are classified. The cycle and rate performance of Li(Ni〈sub〉0.6〈/sub〉Mn〈sub〉0.2〈/sub〉Co〈sub〉0.2〈/sub〉)O〈sub〉2〈/sub〉 cathode material could be improved obviously through Ti〈sub〉3〈/sub〉C〈sub〉2〈/sub〉(OH)〈sub〉2〈/sub〉 modification in an extreme environment, and especially in sub-zero environment.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): Kenji Yoshii, Naoshi Ikeda〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Dielectric and magnetocaloric measurements are carried out for the chromite TmCrO〈sub〉3〈/sub〉. This oxide was reported to be multiferroic below the Néel temperature (〈em〉T〈/em〉〈sub〉N〈/sub〉) of ∼125 K, likely due to a structural transformation. The dielectric response shows large dielectric constants below 300 K. However, from the analyses of loss tangent, AC conductivity and dielectric modulus, this behavior is rooted in hopping of charge carriers rather than electric dipoles, as proposed for some other chromites. No dielectric anomaly is found at 〈em〉T〈/em〉〈sub〉N〈/sub〉. The magnetocaloric effect shows that the magnetic transitions at 〈em〉T〈/em〉〈sub〉N〈/sub〉 as well as the spin reorientation temperature are of a second order. This result strongly suggests the absence of magnetostructural transition at 〈em〉T〈/em〉〈sub〉N〈/sub〉 in accord with no observation of ferroelectric transition at this temperature.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): Rattiya Hongtong, Panya Thanwisai, Rattakarn Yensano, Jeffrey Nash, Sutham Srilomsak, Nonglak Meethong〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Core-shell olivine-type electrospun and doped LiFePO〈sub〉4〈/sub〉/FeS/C composite fibers were synthesized via a single-step process employing an electrospinning method using LiOH·H〈sub〉2〈/sub〉O, metal sul phates, H〈sub〉3〈/sub〉PO〈sub〉4〈/sub〉, citric acid, and polyvinylpyrrolidone (PVP) as the starting materials. Electron microscopy studies showed that the mean diameter of the core-shell composite fibers was about 280 ± 20 nm with a LiFePO〈sub〉4〈/sub〉 phase forming a core with a diameter of about 100 ± 20 nm and a carbon shell with a thickness of 80 ± 20 nm. An FeS phase was formed by a direct reduction of iron (II) sulfate (FeSO〈sub〉4〈/sub〉) that was evenly distributed within the core region of the composite fibers and further improved the electronic conductivity of the fibers. Na〈sup〉1+〈/sup〉, Mg〈sup〉2+〈/sup〉, and Al〈sup〉3+〈/sup〉 doping ions affected fiber morphology and electrochemical performance. All composite fibers showed excellent electrochemical performance. However, Al〈sup〉3+〈/sup〉 ions improved the electrochemical performance of the composite fibers to a significantly greater degree than Na〈sup〉1+〈/sup〉 and Mg〈sup〉2+〈/sup〉 doping ions, increasing the electronic and ionic conductivities of the material while maintaining their core-shell composite fiber characteristics.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉Electrospun LiFePO〈sub〉4〈/sub〉/FeS/C and 5% doped 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mi〉L〈/mi〉〈mi〉i〈/mi〉〈mi〉F〈/mi〉〈msubsup〉〈mrow〉〈mi〉e〈/mi〉〈/mrow〉〈mrow〉〈mn〉1〈/mn〉〈mo linebreak="badbreak"〉−〈/mo〉〈mrow〉〈mo stretchy="false"〉(〈/mo〉〈mi〉n〈/mi〉〈mi〉x〈/mi〉〈mo linebreak="badbreak"〉/〈/mo〉〈mn〉2〈/mn〉〈mo stretchy="false"〉)〈/mo〉〈/mrow〉〈/mrow〉〈mrow〉〈mn〉2〈/mn〉〈mo linebreak="badbreak"〉+〈/mo〉〈/mrow〉〈/msubsup〉〈msubsup〉〈mrow〉〈mi〉M〈/mi〉〈/mrow〉〈mrow〉〈mi〉x〈/mi〉〈/mrow〉〈mrow〉〈mi〉n〈/mi〉〈mo linebreak="badbreak"〉+〈/mo〉〈/mrow〉〈/msubsup〉〈mi〉P〈/mi〉〈msub〉〈mrow〉〈mi〉O〈/mi〉〈/mrow〉〈mrow〉〈mn〉4〈/mn〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉/FeS/C (M = Na〈sup〉1+〈/sup〉, Mg〈sup〉2+〈/sup〉, Al〈sup〉3+〈/sup〉) composites with a unique core-shell structure were synthesized via a simple single-step process to improved electrochemical properties for high performance and low cost Li-ion batteries.〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925838819324946-fx1.jpg" width="287" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): L.V.B. Diop, O. Isnard〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The effects of Fe substitution on the structural and magnetic properties of the HoCo〈sub〉12-〈em〉x〈/em〉〈/sub〉Fe〈sub〉〈em〉x〈/em〉〈/sub〉B〈sub〉6〈/sub〉 (0 ≤ 〈em〉x〈/em〉 ≤ 2) series of intermetallic compounds have been studied. All of the compounds form in the rhombohedral SrNi〈sub〉12〈/sub〉B〈sub〉6〈/sub〉-type structure, the lattice constants increasing linearly with 〈em〉x〈/em〉. These compounds are ferrimagnets with a small transition metal magnetic moment and exhibit a spin reorientation transition. The Curie temperature decreases from 147 K for 〈em〉x〈/em〉 = 0–105 K for 〈em〉x〈/em〉 = 2. The Fe for Co substitution leads also to a progressive decrease of the spontaneous magnetization. The spin reorientation transition temperature is significantly reduced upon Fe for Co substitution whereas the compensation temperature is much less sensitive to the Fe composition.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): Maxim S. Likhanov, Vladislav O. Zhupanov, Valeriy Yu Verchenko, Andrei A. Gippius, Sergei V. Zhurenko, Alexey V. Tkachev, Dina I. Fazlizhanova, David Berthebaud, Andrei V. Shevelkov〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We present a new Fe〈sub〉1–〈em〉x〈/em〉〈/sub〉Re〈sub〉〈em〉x〈/em〉〈/sub〉Ga〈sub〉3〈/sub〉 solid solution, in which a 5〈em〉d〈/em〉-metal––rhenium––partially substitutes for iron to the limiting composition of 〈em〉x〈/em〉 = 0.10. The crystal structure refined for the composition Fe〈sub〉0.91〈/sub〉Re〈sub〉0.09〈/sub〉Ga〈sub〉3〈/sub〉 shows the expected increase in the unit cell parameters compared to the parent FeGa〈sub〉3〈/sub〉 compound, however the M–M (M = Fe, Re) distance decreases within the M–M dumbbell, indicating an increased M–M bonding density. Therein, investigation of the local structure by means of 〈sup〉69,71〈/sup〉Ga NQR spectroscopy revealed the formation of homonuclear Fe–Fe and Re–Re dumbbells. Transport and thermoelectric properties have been investigated for the Re-substituted FeGa〈sub〉3〈/sub〉. Electrical transport measurements showed preservation of the nonmetallic conductivity of Fe〈sub〉1–〈em〉x〈/em〉〈/sub〉Re〈sub〉〈em〉x〈/em〉〈/sub〉Ga〈sub〉3〈/sub〉 despite the decrease of the valence electron concentration from 17 to 16.9 electrons per formula. At low temperatures, Fe〈sub〉1–〈em〉x〈/em〉〈/sub〉Re〈sub〉〈em〉x〈/em〉〈/sub〉Ga〈sub〉3〈/sub〉 is a 〈em〉p〈/em〉-type semiconductor with the band gap of 0.4 eV, but with increasing temperature the sign of the dominant charge carriers changes. Owing to the alloying effect, Fe〈sub〉1–〈em〉x〈/em〉〈/sub〉Re〈sub〉〈em〉x〈/em〉〈/sub〉Ga〈sub〉3〈/sub〉 displays 1.5 times lower thermal conductivity than FeGa〈sub〉3〈/sub〉, which increases at high temperatures because of the growing contribution of the electronic term.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925838819325198-fx1.jpg" width="454" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): Jiashu Zhang, Weiyao Zhao, Zhenjie Feng, Jun-Yi Ge, Jincang Zhang, Shixun Cao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We report the crystal growth, structure analysis and magnetic phase transitions in the single crystal Sm〈sub〉0.15〈/sub〉Dy〈sub〉0.85〈/sub〉FeO〈sub〉3〈/sub〉. The high-quality of the crystal is verified by X-ray diffraction technique. Our research reveals that: 1) the iron sublattice spin reorientation (SR) transition emerges at 25 K, and ends at 10 K; 2) the rare earth antiferromagnetic (AF) order transition happens at 2.6 K; 3) there is a special wasp-waist hysteresis loop at low temperatures. Knowledge of such phase transitions in rare earth orthoferrite system is of potential importance for applications and theoretical studies.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): Yuliang Jiang, Xueyan Fu, Zidong Zhang, Wei Du, Peitao Xie, Chuanbing Cheng, Runhua Fan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Carbon nanofibers embedded with magnetic Fe〈sub〉3〈/sub〉C nanoparticles have been synthesized using electrospinning technique, followed by one-step carbonization. By using Fe〈sub〉3〈/sub〉C/C nanofibers as filler with 10% content, the sample can achieve a minimum reflection loss (RL) of −54.94 dB with a thickness of 1.36 mm, as well as the broad effective absorption bandwidth (EAB) can reach to 4.5 GHz (13.3–17.8 GHz) at the thickness of 1.55 mm. The superior properties might be due to the synergistic effects of dielectric loss, magnetic loss, multiple scattering and reflection. This work presents a facile and promising method to produce high performance microwave absorption materials with thin thickness, light weight and strong absorption.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): E.J. Pickering, K.A. Christofidou, H.J. Stone, N.G. Jones〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In order to reduce the environmental impact of air travel, it is desirable that the efficiencies of gas turbine engines are increased. One way to achieve this goal is to increase the operating temperatures of the engine cores. Unfortunately for aero-engine manufacturers, the temperature capability limits of the Ni-base superalloys used currently have been reached. Hence, new alloys need to be developed that are capable of operating at significantly higher temperatures. In this article, the potential of tantalum-base superalloys is discussed and explored. A suite of alloys based on the Ta-Al-Co system was investigated. It was found that an array of fine carbide precipitates was formed in the Ta-rich matrix in a subset of the alloys, which is promising in terms of developing a strong and damage-tolerant microstructure, but that the elemental partitioning of Al out of the matrix accompanying precipitation is likely to degrade environmental resistance. Nevertheless, it is believed that the design principles described have the potential to facilitate the development of the next generation of high-temperature alloys based on systems of this type.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): C.Q. Zhou, Q.A. Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In order to understand the effect of Pr〈sub〉3〈/sub〉Al〈sub〉11〈/sub〉 nanoparticles on crystallite growth kinetics of nanocrystalline Mg, the crystallite growth characteristics in a Mg−Pr〈sub〉3〈/sub〉Al〈sub〉11〈/sub〉 composite and a pure Mg sample were comparatively investigated in this work. The crystallite growth exponents of nanocrystalline Mg in the Mg−Pr〈sub〉3〈/sub〉Al〈sub〉11〈/sub〉 composite and pure Mg were determined as 〈em〉n〈/em〉 = 5 and 〈em〉n〈/em〉 = 4, respectively. Meanwhile, the activation energy for crystallite growth in Mg−Pr〈sub〉3〈/sub〉Al〈sub〉11〈/sub〉 composite was calculated to be 118.8 kJ/mol, which is higher than 97.1 kJ/mol in pure nanocrystalline Mg. Further studies reveal that the rise of crystallite growth exponent and increase of activation energy in the Mg−Pr〈sub〉3〈/sub〉Al〈sub〉11〈/sub〉 composite are primarily attributed to the pinning effect of Pr〈sub〉3〈/sub〉Al〈sub〉11〈/sub〉 nanoparticles at crystallite boundaries of Mg.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): Liming Tan, Yunping Li, Wenkai Deng, Yong Liu, Feng Liu, Yan Nie, Liang Jiang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Three Ni-base powder metallurgy superalloys have been developed recently, and tensile tests at temperatures ranging from room temperature (RT) to 815 °C were conducted on them. The results conformed their excellent tensile properties, in comparison with several other existed polycrystalline superalloys. In this work, by means of microstructure characterization, thermal dynamic calculations, and theoretical modeling, different strengthening mechanisms including precipitation strengthening, grain boundary strengthening, solid solution strengthening, and Orowan strengthening, were found to contribute to the yield strength in different degrees, which would help to further enhance the tensile properties of these alloys through composition design and processing optimization thereafter.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925838819324892-fx1.jpg" width="459" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica, Volume 164〈/p〉 〈p〉Author(s): Hao-Yang Peng, Wei-Dong Liu, Shi-Jie Liu, Hai-Long Zhang, Wei-Yong Zhou〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Methane-air Continuous Rotating Detonation (CRD) has been firstly achieved in this paper in the hollow chamber with a Laval nozzle, and the diameter of the chamber is just 100 mm. The contraction ratio of the Laval nozzle is a key factor for the CRD realization. CRD can only be obtained when the contraction ratio is no less than 4, but its ER operating range decreases in the increase of contraction ratio from 4 to 10. For all the success cases, the average propagation frequency and velocity are in the ranges of 5.32–5.65 kHz and 1670.48–1774.10 m/s, respectively, and the velocity deficits are less than 10%. Based on the high-speed photography images, the approach of chemiluminescence intensity integral is proposed in this paper, and the propagation characteristics of the flame are analyzed quantitatively. The propagation velocities of the flame and shock wave are agreed well with each other, indicating that the typical feature of detonation wave, i.e., the coupling of the flame and the shock wave, is verified quantitatively.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 5 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica〈/p〉 〈p〉Author(s): Jie Huang, Wei-Xing Yao, Ning Qin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The spiked blunt body is usually adopted to reduce the aerodynamic heating of hypersonic vehicles. In this paper, the heat reduction mechanism of hypersonic spiked blunt body with installation angle at large angle of attack is studied by the CFD numerical method. The AUSM+ scheme and Menter's SST 〈em〉k〈/em〉-〈em〉ω〈/em〉 turbulent model are adopted for the spatial discretization and turbulent simulation respectively. The results show that the maximum wall heat flux of blunt body is sensitive to the angle of attack. The increase of angle of attack causes the aerodynamic heating to rise sharply. The installation angle of the spike can effectively reduce the maximum heat flux of blunt body at large angle of attack, which is very beneficial to the thermal protection of blunt body. There is an optimal installation angle to minimize the maximum heat flux of blunt body. The optimal installation angle is about 1.5° greater than the angle of attack. All the investigations in this paper show the feasibility and advantages of spiked blunt body with installation angle in the engineering applications.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): Christopher S. Daniel, Peter D. Honniball, Luke Bradley, Michael Preuss, João Quinta da Fonseca〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The properties and performance of Zr-2.5 Nb alloys are strongly influenced by their crystallographic texture. As in similar Ti alloys, the texture evolution during hot-processing depends on the complex interactions between the α and β phases and involves deformation, annealing and phase transformation. Although the effect of temperature and deformation has been studied for extruded tube in this alloy, there is no data for texture development during rolling. There is some rolling data for Ti-64 (Ti–6Al–4V), but it is usually for just one of the phases and for a limited set of temperatures. We carried out hot-rolling trials from 700 °C–900 °C to reductions of 50%, 75% and 87.5% and found that the texture in both phases strengthens sharply before the β-transus and when both phases are present in similar amounts. At this point, the texture in α is a strong 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mn〉0002〈/mn〉〈mo〉|〈/mo〉〈mo〉|〈/mo〉〈mtext〉TD〈/mtext〉〈/mrow〉〈/math〉 and the texture in β a strong 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.svg"〉〈mrow〉〈mrow〉〈mo stretchy="true"〉{〈/mo〉〈mrow〉〈mn〉001〈/mn〉〈/mrow〉〈mo stretchy="true"〉}〈/mo〉〈/mrow〉〈mrow〉〈mo〉〈〈/mo〉〈mrow〉〈mn〉110〈/mn〉〈/mrow〉〈mo〉〉〈/mo〉〈/mrow〉〈/mrow〉〈/math〉 rotated cube component. The results suggest there might be a synergistic effect between the two components, which includes dynamic phase transformation. The texture evolution towards stable α 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.svg"〉〈mrow〉〈mrow〉〈mo stretchy="true"〉{〈/mo〉〈mrow〉〈mn〉11〈/mn〉〈mrow〉〈mover accent="true"〉〈mn〉2〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈mn〉0〈/mn〉〈/mrow〉〈mo stretchy="true"〉}〈/mo〉〈/mrow〉〈mrow〉〈mo〉〈〈/mo〉〈mrow〉〈mn〉10〈/mn〉〈mrow〉〈mover accent="true"〉〈mn〉1〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈mn〉0〈/mn〉〈/mrow〉〈mo〉〉〈/mo〉〈/mrow〉〈/mrow〉〈/math〉 or 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.svg"〉〈mrow〉〈mrow〉〈mo stretchy="true"〉{〈/mo〉〈mrow〉〈mn〉11〈/mn〉〈mrow〉〈mover accent="true"〉〈mn〉2〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈mn〉1〈/mn〉〈/mrow〉〈mo stretchy="true"〉}〈/mo〉〈/mrow〉〈mrow〉〈mo〉〈〈/mo〉〈mrow〉〈mn〉10〈/mn〉〈mrow〉〈mover accent="true"〉〈mn〉1〈/mn〉〈mo〉¯〈/mo〉〈/mover〉〈/mrow〉〈mn〉0〈/mn〉〈/mrow〉〈mo〉〉〈/mo〉〈/mrow〉〈/mrow〉〈/math〉 crystallographic components and their final intensity depend on the starting texture. Texture was measured using electron-backscatter diffraction (EBSD) over large areas, with a β reconstruction software used to determine the high temperature β orientations. The texture development in Zr-2.5Nb appears similar to that reported for rolled Ti-64 at temperatures with equivalent phase fractions, although it is difficult to compare the two because of the lack of a titanium dataset as detailed as the one presented here.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925838819324351-fx1.jpg" width="248" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): E.M.M. Ibrahim, M.A.A. Mohamed, H.M. Ali, Vyacheslav O. Khavrus, Silke Hampel, M.M. Wakkad〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Hydrothermal synthesis as a commonly bottom-up growth method has considerable advantages for manufacturing thermoelectric nanomaterials with advanced thermoelectric properties. However, the hydrothermally synthesized thermoelectric nanostructures often show a low thermoelectric performance due to their low power factor. In this work, we report on using a hydrothermal method for the growth of n-type Bi〈sub〉2-x〈/sub〉Sb〈sub〉x〈/sub〉Se〈sub〉3〈/sub〉 nanoflakes with a fixed thickness of ∼16 quintuple-layers. The controlling of the stoichiometric composition, phase purity and crystallinity of the Bi〈sub〉2-x〈/sub〉Sb〈sub〉x〈/sub〉Se〈sub〉3〈/sub〉 nanoflakes are demonstrated by the X-ray diffraction, Raman spectroscopy, and high resolution transmission electron microscopy. We further prove that adding of antimony into Bi〈sub〉2〈/sub〉Se〈sub〉3〈/sub〉 compound mostly influences the in-plane vibration mode. The optical energy gap is sharply increased as the Sb content increases. The effect of the antimony incorporation on the electrical conductivity, Seebeck coefficient and power factor of Bi〈sub〉2-x〈/sub〉Sb〈sub〉x〈/sub〉Se〈sub〉3〈/sub〉 nanoflakes is systematically investigated. The Bi〈sub〉1.92〈/sub〉Sb〈sub〉0.08〈/sub〉Se〈sub〉3〈/sub〉 sample is found to have the highest power factor ∼13.17 μW/cm.K〈sup〉2〈/sup〉 at 470 K which is much higher than those published for other various nanostructured or bulk Bi〈sub〉2〈/sub〉Se〈sub〉3〈/sub〉 compounds. The results propose a great prospect for further enhancing the thermoelectric power factor of the Bi〈sub〉2〈/sub〉Se〈sub〉3〈/sub〉 nanostructures synthesized by this hydrothermal method. Taking into consideration the progress in Bi–Se compounds, the results of this work advocate the promise of Bi–Se nanostructures towards producing high performance thermoelectric devices.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): Javed Rehman, Roshan Ali, Nisar Ahmad, Xiaodong Lv, Chunlei Guo〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉It poses a great challenge to design anode materials with large capacity, excellent cyclic stability and high rate performance. In this paper, through first principle calculations, we computed electronic properties of monolayer WSe〈sub〉2〈/sub〉 with and without strain effects. Our results show that the electronic band gap decreases with strain percent. At 0% tensile strain the value of the band gap is 1.4 eV while at 10% tensile strain the band gap decreases to 0.7 eV. Therefore, the strain effect enhances the electronic conductivity and leads to an increase in the charge carrier transport. In addition, our predictions show that the adsorption energy increases with the strain. Finally, we computed the diffusion barrier for the migration of Li on the surface of a strain engineered WSe〈sub〉2〈/sub〉 monolayer. The lower barrier energy (0.24 eV) reveals that Li can easily overcome this barrier. Our results show that the strain-engineered WSe〈sub〉2〈/sub〉 monolayers are promising anode material for Li-ion battery.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 805〈/p〉 〈p〉Author(s): Seyedeh Marjan Bararpour, Hamed Jamshidi Aval, Roohollah Jamaati〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉AA5083 and AA5052 alloys were utilized as consumable rod and substrate, respectively, in Friction Surfacing (FS) process and a three-dimensional finite element software known as ABAQUS was employed to anticipate the materials thermo-mechanical behavior over this procedure. At that point, in order to investigate the mechanical and microstructures characteristics of the coated samples, the experimental observations and model predictions have been implemented. The results clarified that the strain rate and temperature values are not high at the interface of the substrate and coating layer, also, we observed their maximum values in a layer nearby the upper surface of the coating in the advancing side (AS). Regardless of the irregular strain rate and temperature profiles, there are no important differences in the microstructure of the materials detected in the center of the cross-sections in the direction of advancing and retreating sides (RS). It should be noted that the grain structure is not influenced by the strain energy effect which is kept in the coating layer all through the FS procedure. Moreover, we can consider the grain structure recrystallization as a contributing factor in improving the material strength of the coating which is anticipated to be proportional to the grain size in reverse.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): Aref Alqahtani, Shahid Husain, Anand Somvanshi, Wasi Khan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Perovskite-type GdCr〈sub〉1-〈em〉x〈/em〉〈/sub〉Mn〈sub〉〈em〉x〈/em〉〈/sub〉O〈sub〉3〈/sub〉 (0.0 ≤ 〈em〉x〈/em〉 ≤ 0.4) nano-crystalline samples are synthesized using sol-gel auto combustion process. The effect of Mn-doping in GdCrO〈sub〉3〈/sub〉is investigated in term of structural, morphological, optical and thermal properties. X-ray diffraction (XRD) patterns confirm orthorhombic crystal structure of all the samples. The lattice parameters bond lengths and bond angles as obtained from Rietveld refinement analysis are found to vary systematically with Mn concentration. The crystallite sizes as calculated from the Scherrer's equation are found to decrease with Mn content. The Williamson-Hall (W–H) analysis reveals that the crystallite sizes decrease whereas lattice strain, stress, and energy density become more with the increase in Mn doping except for 〈em〉x〈/em〉 = 0.3.The particle size estimated using transmission electron microscopy (TEM) are consistent with that obtained through W–H analysis. Scanning electron microscopy (SEM) images with energy dispersive x-ray (EDX) analysis exhibit significant change in the surface morphology with Mn doping and ensure the elemental compositions of the samples. The Fourier transform infrared (FTIR) spectra of these samples confirm the formation of desired crystal structure with two main characteristic bands at 476 and 586 cm〈sup〉−1〈/sup〉. The optical band gap is found to reduce whereas Urbach energy increases with the increase in Mn concentration. The values of refractive index decrease in the ultraviolet region as a function of wavelength for all the samples and minimizes at the main absorption peak position as observed in the UV/Vis. spectra. The value of heat capacity at constant pressure (〈em〉C〈/em〉〈sub〉〈em〉p〈/em〉〈/sub〉) decreases with Mn doping except for 30% Mn concentration. Therefore, the present investigation suggests that the properties of GdCrO〈sub〉3〈/sub〉 system can be tuned with the appropriate doping of Mn for the potential applications.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 805〈/p〉 〈p〉Author(s): Xinghua Zhu, Qingshuang Xie, Haibo Tian, Ming Zhang, Zongyan Gou, Shuai He, Peng Gu, Haihua Wu, Jitao Li, Dingyu Yang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Usually, ZnO thin films used in ultraviolet photodetector exhibit good photoresponse property when ultraviolet signal is strong enough. However, due to the high dark current, pure ZnO is insusceptible to weak ultraviolet signal. To address this problem, lithium-doped ZnO (LZO) thin films were prepared using the sol-gel method in this study. Results revealed that the LZO thin film doped with low concentration (2 at.%) had a dark current about 10 times lower than the pure ZnO. In addition, the ultraviolet with a low irradiance of 90 μW/cm〈sup〉2〈/sup〉 was used. According to the results of the investigations on the external quantum efficiency and responsivity, the inherent photocurrent generation ability of ZnO was not deteriorated through low concentration lithium doping. LZO thin film doped with 2 at.% exhibited a high sensitivity to weak ultraviolet signal --- the signal-to-noise ratio was enhanced by approximately 10 times compared with that of pure ZnO. This study indicates that LZO thin films with low doping concentration are promising application on weak ultraviolet signal photodetector.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 805〈/p〉 〈p〉Author(s): Jian Lan, Weidong Xuan, Yu Han, Yongshun Li, Huaizhou Wu, Wei Shao, Chuanjun Li, Jiang Wang, Zhongming Ren〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The effect of hot isostatic pressing on the tensile property of single crystal superalloys at elevated temperature is studied experimentally. The results show that the high temperature elongation of nickel based single crystal superalloys is obviously enhanced by hot isostatic pressing, while the yield strength is unchanged. Besides, it is found that the hot isostatic pressing causes the change of fracture surface. The enhancement of elongation and the change of fracture behavior are discussed.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 805〈/p〉 〈p〉Author(s): Z.M. Li, X.N. Li, C.Y. Wang, Y.H. Zheng, Q.X. Yu, X.T. Cheng, N.J. Li, L.X. Bi, Q. Wang, C. Dong〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The heat resistance of copper alloys is desirable to improve while it services at high temperature as electrically and thermally conductive components. In present paper, the strengthening pattern of nickel-based superalloys is expected to be applied in copper alloys. Here the Cu〈sub〉50〈/sub〉Ni〈sub〉37.5〈/sub〉〈em〉M〈/em〉〈sub〉12.5〈/sub〉 (〈em〉M〈/em〉 = Al, Cr, Mo) alloys were prepared by vacuum arc melting and heat-treated in the corresponding conditions to obtain three different kinds of typical microstructure. The room temperature (RT) properties (hardness and resistivity) and high temperature properties (melting point, softening temperature and variable temperature resistivity) of the three alloys are contrasted and analyzed in detail. The Cu〈sub〉50〈/sub〉Ni〈sub〉37.5〈/sub〉Al〈sub〉12.5〈/sub〉 alloy strengthened through the γ′ phase coherent precipitation shows the best conductivity and highest hardness (5.47 %IACS (International Annealed Copper Standard) and 310.1 HV). The splitting of the γ′ phase is contributing to hardening at high aging temperature. The resistivity-temperature behavior of the three alloys shows that the resistivity with rising temperature consists of the ideal lattice resistivity and the resistivity increment due to the defects. The Cu〈sub〉50〈/sub〉Ni〈sub〉37.5〈/sub〉Al〈sub〉12.5〈/sub〉 alloy has the smallest room temperature resistivity and its resistivity maintains the lowest during the whole heating process (RT-1077K). Therefore, the coherent precipitated γ′ phase is expected to improve the heat resistance of the copper alloys while maintaining its electrical conductivity.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925838819325708-fx1.jpg" width="282" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 805〈/p〉 〈p〉Author(s): Cui-Ning Feng, Xiao-Ye Zhan, Pan Li, Xiao-Feng Guo, Dan Li, Xiu-Cheng Zheng, Guang-Ping Zheng〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Glucose-derived porous activated carbon materials (AGC-600-4 and AGC-180-〈em〉x〈/em〉) are prepared using ZnCl〈sub〉2〈/sub〉 as the etching agent via impregnation treatment and hydrothermal method followed by the calcination process. The analytic results indicate that the obtained materials exhibit higher specific surface area and superior double-layer capacitive behavior than the corresponding pristine carbon (GC-600 and GC-180) when used as electrode materials for supercapacitors. Moreover, compared with the AGC-600-4 nanosheets, the optimal AGC-180-4 microspheres have a high specific surface area of 1713 m〈sup〉2〈/sup〉 g〈sup〉−1〈/sup〉 and a maximum specific capacitance of 235.9 F g〈sup〉−1〈/sup〉 at a current density of 1.0 A g〈sup〉−1〈/sup〉 in the three-electrode system. Meanwhile, AGC-180-4 also exhibits better capacitive properties than AGC-600-4 in the two-electrode system, showing an excellent cyclic stability with a high energy density of 24.63 Wh kg〈sup〉−1〈/sup〉 at the power density of 949.5 W kg〈sup〉−1〈/sup〉. It is thus demonstrated that AGC-180-4 could be ideal electrode materials for supercapacitor due to its unique etched spherical structure and excellent electrochemical properties.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925838819325903-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 805〈/p〉 〈p〉Author(s): Ilham Bezza, Erwann Luais, Fouad Ghamouss, Mustapha Zaghrioui, François Tran-van, Joe Sakai〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉An 〈em〉in-situ〈/em〉 temperature-controlled Raman spectroscopy aided unique electrode fabrication technique has been developed for Li-ion battery applications, ensuring superior electrochemical quality of the multi-porous LiCoO〈sub〉2〈/sub〉 films with higher stoichiometric purity of high temperature (HT)-LiCoO〈sub〉2〈/sub〉 phase, by observing the structural changes during the fabrication process and thus confirming the transformation from the low temperature (LT)-LiCoO〈sub〉2〈/sub〉 phase. This much desired simple process is not only free of any sort of binders or carbon additives but also works at atmospheric pressure, leading to a very simple deposition technique using a homemade and inexpensive set-up. Also, the time of depositions were varied and resultant films we investigated for their electrochemical performance. The high-resolution scanning electron microscope (SEM) observation has revealed not only a μm-size porous structure but also three-dimensional cross-link with 10 nm-level pores of the material, which ensured the much-desired porosity for high-performance cathodes.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 805〈/p〉 〈p〉Author(s): S.C. Ram, K. Chattopadhyay, I. Chakrabarty〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Functionally graded in-situ A356-Mg〈sub〉2〈/sub〉Si composites by centrifugal casting method have been studied with varying percentage of extra Mg additions during synthesis. The coarse primary Mg〈sub〉2〈/sub〉Si particles and the Si morphology in eutectic do not yield appreciable mechanical properties. Solution treatment and artificial ageing (T6) are effective means to improve mechanical properties by refining the as-cast structure with additional formation of very fine precipitates during ageing. The microstructural evolution has been assessed by optical, scanning and transmission electron microscopy and X-ray diffraction analysis. Ageing curves are plotted with hardness versus ageing time. High temperature tensile properties are evaluated at room temperature, 150 °C and 300 °C at different layers of the graded composites and are compared between as-cast and T6 conditions. The tensile fracture mechanisms are explained from fractographs. A remarkable improvement in high temperature tensile strength at 150 °C with adequate ductility is observed in T6 condition with respect to as-cast condition.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925838819325721-fx1.jpg" width="264" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 805〈/p〉 〈p〉Author(s): Taiqian Mo, Zejun Chen, Boxin Li, Hongtao Huang, Weijun He, Qing Liu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The impact of strain path on microstructure and mechanical properties in AA1100/AA7075 laminated metal composite was investigated in present work. The results indicate that the plastic instabilities occurred in the hard layer can be inhibited effectively and the mechanical properties of the composite were improved obviously after the cross rolling (CR) process. The formation of continuous and straight interface was attributed to the difference in flow properties between the constituent layers was decreased after CR process. It is found that the strain path change during CR results in the typical rolling texture is shifted from the ideal Brass (110)〈112〉 along the 〈em〉α〈/em〉-fiber to the near ND-rotated Brass (011)〈755〉 component, promoting a better mechanical isotropy of the AA1100/AA7075 laminated metal composite. In addition, the Al/Al alloy laminated metal composite with continuous layer structure exhibits better load-bearing capacity in hard layers than the wave layer structure during deformation, which is a main reason for increasing of the strength.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 5 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 804〈/p〉 〈p〉Author(s): N. Patra, C.L. Prajapat, P.D. Babu, S. Rai, S. Kumar, S.N. Jha, D. Bhattacharyya〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Heusler alloy of Co〈sub〉2〈/sub〉FeSi (CFS) is a promising candidate for spintronics applications due to its high magnetic moment and high spin polarization. In this report two series of CFS thin films of approximate thickness of 1000 Å were prepared using Pulsed Laser Deposition (PLD) technique by two separate routes, viz., (i) by depositing at elevated substrate temperature and (ii) by depositing at room temperature followed by post-deposition annealing under vacuum. The effects of these two thermal growth processes on the structural and magnetic properties of the films have been studied in detail here. X-ray diffraction study suggests that similar to the bulk target cubic Heusler phase is maintained in the thin films prepared by both the processes, however, X-ray reflectivity study shows that the films deposited at elevated substrate temperatures have higher density and surface roughness than the other set. Co/Fe atomic ratio in the films was found to remain near stoichiometry up to high temperature in both the series of samples though atomic percentage of Si is found to be higher in the samples. Synchrotron based Extended X-ray absorption fine structure (EXAFS) measurements indicate higher 〈em〉3d-3p〈/em〉 (Co-Si) hybridization for the series of samples prepared at elevated temperature while stronger 3〈em〉d-3d〈/em〉 (Co-Fe) hybridization for the samples prepared with post deposition annealing. EXAFS study also indicated presence of Co/Fe type antisite disorder which increases with increase in the substrate temperature. Finally from detail magnetic measurements it was observed that the films prepared by post-deposition annealing process have lesser crystallinity, magnetic ordering and magneto crystalline anisotropy in comparison to the films grown with elevated substrate heating.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 805〈/p〉 〈p〉Author(s): Hao Guo, Taotao Sun, Liguo Yue, Ning Wu, Qi Li, Wenqing Yao, Wenhu Yang, Wu Yang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉As a kind of energy storage device, supercapacitors have attracted the attention of researchers, and the development of high-performance electrode materials is also the focus of attention. In this paper, template synthesis and pyrolysis were combined to prepare high performance porous carbon electrode materials. The carbonized electrode material effectively increased the capacitance storage capacity and charge transfer rate. The results revealed that the derivative had a relatively low charge-transfer resistance and high specific capacitance of 1059 F·g〈sup〉−1〈/sup〉 at a current density of 1.0 A·g〈sup〉−1〈/sup〉 in a three-electrode system. To further exploring practical application, a device based on the derivative and hemp-activated carbon asymmetric supercapacitor was assembled in 0.1 M Na〈sub〉2〈/sub〉SO〈sub〉4〈/sub〉 neutral electrolyte, which exhibited an energy density of 20.35 Wh·kg〈sup〉−1〈/sup〉 at a power density of 400 W·kg〈sup〉−1〈/sup〉. Interestingly, it showed capability retention of nearly of 91.7% and columbic efficiency of 100% even after 10000 charging/discharging cycles in the neutral electrolyte.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925838819325691-fx1.jpg" width="365" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 30 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 803〈/p〉 〈p〉Author(s): Nejeh Hamdaoui, Yashar Azizian-Kalandaragh, Mouadh Khlifi, Lotfi Beji〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The effect of Cd-doping on physical properties of Ni〈sub〉0.6-〈em〉x〈/em〉〈/sub〉Cd〈sub〉〈em〉x〈/em〉〈/sub〉Mg〈sub〉0.4〈/sub〉Fe〈sub〉2〈/sub〉O〈sub〉4〈/sub〉 spinel ferrite has been investigated. Scanning electron spectroscopy (SEM) confirms the formation of grain and grain boundaries in these samples and the presence of all chemical elements introduced was confirmed by EDS. The X-ray analyses indicate that all the compounds have the cubic structure with 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mi〉F〈/mi〉〈mi〉d〈/mi〉〈mrow〉〈mover accent="true"〉〈mrow〉〈mn〉3〈/mn〉〈/mrow〉〈mo stretchy="true"〉¯〈/mo〉〈/mover〉〈/mrow〉〈mi〉m〈/mi〉〈/mrow〉〈/math〉 space group, cell parameter increase which Cd content. A ferromagnetic state at room temperature for all compounds is detected by a magnetization measurement of hysteresis loops. We note that the saturation magnetization increases with Cd content, however, the remnant magnetization, and the corrective field decreases. DC electrical conductivity analysis shows a semiconductor behavior for all sample. In addition, non-overlapping small polaron tunneling (NSPT) and the overlapping large polaron tunneling (OLPT) are the dominants conductions mechanisms in our samples.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 30 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 803〈/p〉 〈p〉Author(s): Beiyue Ma, Chang Su, Xinming Ren, Zhi Gao, Fan Qian, Wengang Yang, Guoqi Liu, Hongxia Li, Jingkun Yu, Qiang Zhu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Fly ash is a typical industrial solid waste that seriously affects human health and ecological balance. In order to recycle the fly ash, in this work, porous mullite ceramics were successfully fabricated with fly ash and bauxite via reaction synthesis process. Effects of firing temperature (1450–1550 °C), silicon carbide addition amount (0–15 wt%), and potash feldspar addition amount (0–16 wt%) on the mullite porous ceramics were systematically investigated. It was found that increasing the silicon carbide addition amount or raising firing temperature was favourable for improving the cold compressive strength and thermal shock resistance of the porous ceramics. Consequently, the porous ceramics with 10 wt% silicon carbide, 4–12 wt% potash feldspar had optimal overall performances. The closed porosity and cold compressive strength ranges were 14.79%–18.57% and 217.18–236.67 MPa, respectively. The thermal cycles were 7–9 times, and the thermal conductivity was reached to 2.19–2.52 W m〈sup〉−1〈/sup〉 K〈sup〉−1〈/sup〉 at 800 °C. This work provides a convenient and promising method for the utilization of fly ash.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S092583881932362X-fx1.jpg" width="496" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 30 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 803〈/p〉 〈p〉Author(s): Daria N. Vtyurina, Irina A. Kaurova, Galina M. Kuz'micheva, Victor B. Rybakov, Dmitry Yu. Chernyshov, Evgeny V. Khramov, Sergey V. Firstov, Vladimir N. Korchak〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Promising luminescent CsCd〈em〉X〈/em〉〈sub〉3〈/sub〉 (〈em〉X〈/em〉 = Cl, Br) single crystals, both nominally-pure and doped with bismuth, have been studied comprehensively by X-ray diffraction, X-ray synchrotron radiation, and X-ray absorption spectroscopy. Crystal structure refinement shows vacancies in the Cs crystallographic site and partial substitution of Cd〈sup〉2+〈/sup〉 ions by Bi〈sup〉3+〈/sup〉 ones in both CsCdCl〈sub〉3〈/sub〉 and CsCdBr〈sub〉3〈/sub〉 (point defects Bi〈sub〉Cd〈/sub〉〈sup〉•〈/sup〉), which is consistent with the results of X-ray absorption spectroscopy. The assumed presence of Bi〈sup〉1+〈/sup〉 ions in the Cs〈sup〉1+〈/sup〉 sites of doped CsCd〈em〉X〈/em〉〈sub〉3〈/sub〉 (〈em〉X〈/em〉 = Cl, Br) crystals is not confirmed. In the photoluminescence spectra of Bi-doped CsCdCl〈sub〉3〈/sub〉 and CsCdBr〈sub〉3〈/sub〉 crystals, a single band in the near-IR spectral range with a maximum around 1000 nm is caused by point defects Bi〈sub〉Cd〈/sub〉〈sup〉•〈/sup〉. Photoluminescence spectra and decay kinetics of Bi-doped CsCd〈em〉X〈/em〉〈sub〉3〈/sub〉 (〈em〉X〈/em〉 = Cl, Br) indicate their promising use as luminescent materials.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 30 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 803〈/p〉 〈p〉Author(s): Sung-Hsiu Huang, Cheng-Yi Tong, Tsung-Eong Hsieh, Jyh-Wei Lee〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉For the development of advanced nanoscale multilayer protective coatings, proper design of microstructure and chemical composition of carbon containing sequential transition metal nitride nanolayers is an important issue. In this work, five different nanostructured CrCN/ZrCN multilayer coatings were deposited periodically by cathodic arc evaporation. The bilayer period of the CrCN/ZrCN multilayer coatings was kept at 20 nm. The C〈sub〉2〈/sub〉H〈sub〉2〈/sub〉 gas flow ratio was adjusted from 6.3 to 20.0% for achieving CrCN/ZrCN multilayer coatings with 2.3–4.2 at.% carbon content. Nanolaminated CrCN and ZrCN nitride layers and thin amorphous carbon nitride mixed nanolayers ∼5 nm thick were obtained as the carbon content reached 4.2 at.%. It was found that the hardness and adhesion quality were strongly improved by the carbon addition to the CrCN/ZrCN multilayer coatings. An increase of 2.6–4.6 GPa in hardness was found for the CrCN/ZrCN multilayer coatings due to the balance of solution hardening effect of carbon atoms and the softening by the amorphous mixed nanolayer. An optimal combination of high hardness, 28.9 GPa, and good adhesion, 41 N of upper critical load were achieved when the carbon content was 4.2 at.% for the CrCN/ZrCN multilayer coatings.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 30 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 803〈/p〉 〈p〉Author(s): Hanfei Zhu, Yuyao Zhao, Yingying Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Epitaxial BiFeO〈sub〉3〈/sub〉 thin films with (100), (110) and (111) orientations were grown on the SrRuO〈sub〉3〈/sub〉-buffered SrTiO〈sub〉3〈/sub〉 substrates by using an off-axis magnetron sputtering. Unlike the BiFeO〈sub〉3〈/sub〉(110) and BiFeO〈sub〉3〈/sub〉(111) thin films that exhibited a single rhombohedral phase structure, a dominant rhombohedral phase accompanying with a small amount of tetragonal phase was identified in the BiFeO〈sub〉3〈/sub〉(100) thin film. In particular, the leakage currents and ferroelectric polarizations of sputtered BiFeO〈sub〉3〈/sub〉 thin films were focused on and these films showed utterly different current density-electric field (〈em〉J〈/em〉-〈em〉E〈/em〉) behaviors whether in the positive or negative electric field. Among the three films, the ferroelectric polarization of the BiFeO〈sub〉3〈/sub〉(100) thin film presented a good frequency stability and had the maximum remnant polarization of 〈em〉P〈/em〉〈sub〉r〈/sub〉 ∼ 78 μC/cm〈sup〉2〈/sup〉 @ 10 kHz, which could be further demonstrated by pulsed polarizations of films. The distinct differences in electrical properties of orientation-engineered BiFeO〈sub〉3〈/sub〉 thin films in present case can be attributed to their different crystallographic orientations and microstructures.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925838819324405-fx1.jpg" width="329" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 30 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 803〈/p〉 〈p〉Author(s): Lihong Wang, Hongtao Guan, Jianqiao Hu, Qiang Huang, Chengjun Dong, Wei Qian, Yude Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Porous jute biomass carbon (PJBC) composited by Fe〈sub〉3〈/sub〉O〈sub〉4〈/sub〉 nanoparticles were successfully prepared by a chemical coprecipitation method at a low temperature of 60 °C, which is very simple to prepare a high degree of purity of Fe〈sub〉3〈/sub〉O〈sub〉4〈/sub〉 nanoparticles. The structure, morphology, and microwave absorption performances of the Fe〈sub〉3〈/sub〉O〈sub〉4〈/sub〉/PJBC composites were investigated in detail. Due to the porous structure and large interfaces between Fe〈sub〉3〈/sub〉O〈sub〉4〈/sub〉 and PJBC, the Fe〈sub〉3〈/sub〉O〈sub〉4〈/sub〉/PJBC composites show excellent microwave absorption performances. The minimum reflection loss (RL) value of −39.5 dB is obtained for the Fe〈sub〉3〈/sub〉O〈sub〉4〈/sub〉/PJBC composites at the frequency of 6.4 GHz. When the thickness is only 1.6 mm, an effective absorption bandwidth (RL ≤ −10 dB) for 5 GHz is achieved from 13.8 to 17.8 GHz. The excellent microwave absorption performances for the Fe〈sub〉3〈/sub〉O〈sub〉4〈/sub〉/PJBC composites are rooted in enhanced impedance matching, large interfaces, ionic polarization, eddy loss, natural resonance, and multiple reflection and scattering. Consequently, considering market applications and the cost, the Fe〈sub〉3〈/sub〉O〈sub〉4〈/sub〉/PJBC composite in this work can be a promising candidate for microwave absorber.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉Fe〈sub〉3〈/sub〉O〈sub〉4〈/sub〉/PJBC composites prepared by a chemical coprecipitation method at a low temperature of 60 °C exhibit the microwave absorbing performance.〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S092583881932448X-fx1.jpg" width="476" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 30 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 803〈/p〉 〈p〉Author(s): N.E. Dubinin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The concentration dependencies of the self-diffusion coefficients in liquid Na–K and K–Cs alloys at 〈em〉T〈/em〉 = 373 K are calculated in the framework of the linear trajectory approximation in conjunction with the square-well (SW) model treated by the mean spherical approximation in the semi-analytical representation. It is shown that this approach allows to achieve a good description of diffusion properties for liquid binary metal alloys at the same values of the SW parameters that lead to a good description of the structure and entropy for alloys under consideration.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 30 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 803〈/p〉 〈p〉Author(s): Xiang Wu, Richu Wang, Chaoqun Peng, Yan Feng, Zhiyong Cai〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Gas atomized Cu-3Ag-0.5Zr and Cu-3Ag-0.5Zr-0.4Cr-0.35Nb (wt.%) powders were compacted by hot isostatic pressing (HIP) and followed by forging. The microstructures and tensile properties at room and elevated temperatures (400 °C, 450 °C and 500 °C) were investigated. The continuous Ag precipitates (5–25 nm) and Cu〈sub〉4〈/sub〉AgZr (200–500 nm) particles are the main strengthening phases in the Cu-3Ag-0.5Zr alloy. The yield strength and ultimate tensile strength at room temperature are enhanced by 104 MPa and 83 MPa, respectively, due to the introduction of Cr〈sub〉2〈/sub〉Nb (50–80 nm) particles. Besides, the strength at elevated temperatures is also improved. For both the alloys, the discontinuous Ag precipitates near the grain boundaries result in a weak grain boundary cohesion when tested at 450 °C, leading to the lowest elongation. The Cr〈sub〉2〈/sub〉Nb and Cu〈sub〉4〈/sub〉AgZr particles are extremely stable when tested at 500 °C, which benefits to the performance enhancements at elevated temperatures.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 30 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 803〈/p〉 〈p〉Author(s): Wenjing Zhang, Huihong Liu, Hua Ding, Hidetoshi Fujii〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The rolled Ti–15V–3Cr–3Sn–3Al (Ti-15-3) alloy (metastable 〈em〉β〈/em〉 titanium alloy) sheet with an average grain size of 44.0 μm was subjected to friction stir processing (FSP) at a tool rotation speed of 250 rpm and a tool traverse speed of 100 mm/min (250–100). Thereafter, a fine-grained (∼6.6 μm) and relatively equiaxed microstructure with a high angle grain boundary (HAGB) ratio of 74.5% was observed in the stir zone (SZ). Superplastic tensile tests were then conducted on this microstructure at the temperatures ranging from 600 °C to 800 °C and strain rates range of 1 × 10〈sup〉−4〈/sup〉-1 × 10〈sup〉−2〈/sup〉 s〈sup〉−1〈/sup〉, and an excellent low-temperature superplasticity (LTSP) with the elongation of 463% was obtained at 650 °C and 1 × 10〈sup〉−4〈/sup〉 s〈sup〉−1〈/sup〉. In addition, the microstructure in the gauge section of the tensile specimens interrupted at different engineering strains of 20%, 50%, 200%, and 463% (tensile fractured) at the optimal superplastic tensile condition of 650 °C and 1 × 10〈sup〉−4〈/sup〉 s〈sup〉−1〈/sup〉 was studied. It was found that the precipitated 〈em〉α〈/em〉 phase increased with the increasing strain, which contributed to the achievement of an enhanced LTSP by inhibiting the grain growth. Moreover, the α grains with a finer grain size of 4.4 μm was observed in the gauge section of the tensile fractured specimen and this was attributed to the occurrence of continuous dynamic recrystallization (CDRX). Therefore, the superplastic deformation mechanism of the Ti-15-3 alloy is recognized as grain boundaries sliding (GBS) accompanied with dislocation movement and CDRX at 650 °C and 1 × 10〈sup〉−4〈/sup〉 s〈sup〉−1〈/sup〉.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 30 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 803〈/p〉 〈p〉Author(s): G.E. Nikiforova, O.N. Kondrat'eva, A.V. Tyurin, M.A. Ryumin, V.N. Guskov, K.S. Gavrichev〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Lutetium orthotantalate with 〈em〉M′〈/em〉-fergusonite type structure was synthesized using a reverse coprecipitation method. Phase and chemical composition, as well as microstructure of the synthesized sample, were characterized by X-ray diffraction (XRD), μ-X-ray fluorescence and Fourier-transform infrared spectroscopies, and scanning electron microscopy. Heat capacity of 〈em〉M′〈/em〉-LuTaO〈sub〉4〈/sub〉 was first studied by adiabatic and differential scanning calorimetry (DSC) in the temperature range from 10 to 1300 K. Using a temperature dependence of heat capacity, the standard thermodynamic functions (entropy 〈em〉S〈/em〉〈sub〉m〈/sub〉〈sup〉o〈/sup〉(〈em〉T〈/em〉), enthalpy change 〈em〉H〈/em〉〈sub〉m〈/sub〉〈sup〉o〈/sup〉(〈em〉T〈/em〉)〈em〉–H〈/em〉〈sub〉m〈/sub〉〈sup〉o〈/sup〉(0) and derived Gibbs energy 〈em〉Ф〈/em〉〈sub〉m〈/sub〉〈sup〉o〈/sup〉(〈em〉T〈/em〉)) were calculated in the range of 〈em〉T〈/em〉→0–1300 K. The standard molar entropy of 〈em〉M′〈/em〉-LuTaO〈sub〉4〈/sub〉 at 298.15 K is 123.12 ± 0.50 J K〈sup〉−1〈/sup〉 mol〈sup〉−1〈/sup〉. A comparison of the experimental heat capacity values, obtained by DSC, with those calculated using the empirical Neumann-Kopp rule showed a reasonable agreement between the two sets of data only up to ≈1000 K. The high-temperature evolution of the lattice parameters for 〈em〉M′〈/em〉-LuTaO〈sub〉4〈/sub〉 was studied by high-temperature XRD (HTXRD). According to the high-temperature heat capacity study and the HTXRD measurements, there were no phase transformations up to 1300 K. Based on the HTXRD data, the linear and volume thermal expansion coefficients were obtained for the first time.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 30 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 803〈/p〉 〈p〉Author(s): V.I. Voronkova, E.P. Kharitonova, E.I. Orlova, N.I. Sorokina, T.A. Sorokin, A.M. Antipin, E.D. Baldin, V.V. Grebenev〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Undoped and Mg-doped Nd〈sub〉2〈/sub〉MoO〈sub〉6〈/sub〉 oxymolybdate single crystals and polycrystalline samples have been prepared by flux growth and solid-state reactions. The materials have been characterized by X-ray diffraction, EDS microanalysis, X-ray structure analysis, differential scanning calorimetry, thermogravimetry, and impedance spectroscopy. The (MgO)〈sub〉〈em〉x〈/em〉〈/sub〉(Nd〈sub〉2〈/sub〉MoO〈sub〉6〈/sub〉)〈sub〉(1–〈em〉x〈/em〉)/2〈/sub〉 solid solution series has been shown to extend to 〈em〉x〈/em〉 = 0.20. Doping of Nd〈sub〉2〈/sub〉MoO〈sub〉6〈/sub〉 single crystals with Mg leads to splitting of the Mo, Nd1, and O2 sites. A structural model in which the Mg atoms partially substitute for Mo atoms and reside near the Mo site, 0.28 Å from it, ensures the best agreement with the observed diffraction pattern. The conductivity of the undoped and doped polycrystalline samples approaches 10〈sup〉−4〈/sup〉 S/cm at 800 °C and is assumed to have an anionic nature.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925838819324764-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 30 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 803〈/p〉 〈p〉Author(s): Chaocheng Liu, Xucai Kan, Xiansong Liu, Shuangjiu Feng, Jiyu Hu, Wei Wang, Khalid Mehmood Ur Rehman, Mudssir Shezad〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Conventional permanent hexagonal ferrites may prohibit the soft magnetic properties through the effort of doping behavior. A typical case of this magnetic conversion is Co–Ti doped M-type strontium hexaferrites. On the basis of this system, we developed a novel foundation of La doped CoTi-strontium hexaferrites in present work and a promising result were obtained. Polycrystalline Sr〈sub〉1-〈em〉x〈/em〉〈/sub〉La〈sub〉〈em〉x〈/em〉〈/sub〉Fe〈sub〉10〈/sub〉CoTiO〈sub〉19〈/sub〉 (〈em〉x〈/em〉 = 0.00–0.10) hexaferrites present the admirable characteristics as general soft ferrites (high permeability 〈em〉μ〈/em〉, low core loss 〈em〉P〈/em〉〈sub〉cv〈/sub〉), and retain the properties of permanent ferrites simultaneously. This extraordinary performance exhibit more appropriate candidate for multilayer inductors contrast to normal soft magnetic materials. Meanwhile, we presented a series of measurement results to investigate the morphology and texture of the sample, which revealed the internal structural feature systematically.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉Magnetoplumbite crystal structure and spin directions of 2〈em〉a〈/em〉 and 4〈em〉f〈/em〉〈sub〉2〈/sub〉 sites for M-type strontium hexaferrites.〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925838819324235-fx1.jpg" width="278" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: Available online 1 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica〈/p〉 〈p〉Author(s): Gerald R. Harp〈/p〉

Beschreibung: 〈p〉Publication date: 30 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 803〈/p〉 〈p〉Author(s): Min-Su Lee, Yong-Taek Hyun, Tea-Sung Jun〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We have performed macroscopic tensile and nanoindentation tests to investigate the effect of oxygen content on the global and local strain rate sensitivity of grades 1, 2 and 4 commercially pure titanium (CP–Ti). Electron backscatter diffraction (EBSD) was used to characterise the crystallographic texture of target samples and orientation of target grains. Slip activities were anticipated by Schmid factor analysis, indicating the relative incidence of 〈a〉 type prismatic and basal slips in the macroscopic region, and similarity of potential local deformation between comparative grain orientations. Further slip trace analysis around the residual impressions showed similar slip activity in equivalent orientations regardless of oxygen content. Global and local strain rate sensitivity were evaluated with respect to the influence of texture and grain orientations, respectively. Significant oxygen-dependent rate sensitivity is observed such that the rate sensitivity is inverse to the oxygen content and this effect is agreed on at both macro- and microscopic levels. These findings are potentially important for understanding the influence of oxygen content on the dwell fatigue of Ti alloys and correlating the intrinsic mechanism at the microscopic level to the macroscopic deformation behaviours.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925838819324107-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 30 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 803〈/p〉 〈p〉Author(s): Y. Al-Hadeethi, S.A. Tijani〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Nuclear medicine makes use of different gamma emitting radioactive sources which necessitates a reliable way of reducing unnecessary exposure of nuclear medicine personnel and the general public in the vicinity of these radioactive sources. Radiation shielding is one of the major ways through which the medical personnel and the public are protected from the harmful effects of ionizing radiation. A material that combines transparency, non-toxicity and radiation shielding ability is of high interest presently in the medical environment. This work aims to determine the suitability of lead-free transparent 50BaO-(50-x)borosilicate-xBi〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 glass system for radiation shielding purposes at diagnostic nuclear medicine energies and to compare its properties with that of transparent lead glass and ordinary concrete. The results of this work show that while all the glass samples show comparable shielding properties with the lead glass, glass sample G5 is the best lead glass substitute. All the studied glasses are lighter than lead glass and showed better shielding properties than ordinary concrete.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 30 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 803〈/p〉 〈p〉Author(s): Liang Zheng, Wenjie Zhang, Qi Wang, Hong Zhang, Zhou Yu, Cuihua Cheng, Yong Zhang, Ming Lei, Yong Zhao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉MgB〈sub〉2〈/sub〉 bulks with NaCl doping amount ranging from 0–30 at% have been prepared by hot pressed sintering process. With the increase of NaCl doping amount, the 〈em〉c〈/em〉 axis lattice parameter of MgB〈sub〉2〈/sub〉 monotonously increases, indicating the substitution of Mg atoms by larger Na atoms. Meanwhile, the intensity of diffraction peaks of both NaCl and impurity phase of MgO increases. More compact morphology was found in the NaCl doped MgB〈sub〉2〈/sub〉 samples. The critical transition temperature (〈em〉T〈/em〉〈sub〉c〈/sub〉) decreases from 38.2 K to 36.8 K with the increase of NaCl doping amount from 0 to 30 at%, and the corresponding transition width of 〈em〉T〈/em〉〈sub〉〈em〉c〈/em〉〈/sub〉 (Δ〈em〉T〈/em〉〈sub〉c〈/sub〉) increases from 0.5 K to 1.8 K. When the doping amount of NaCl is not exceeding 10 at%, the 〈em〉J〈/em〉〈sub〉c〈/sub〉 value is about 10〈sup〉6〈/sup〉 A/cm〈sup〉2〈/sup〉 at 4.2 K, 3 T, and 5 × 10〈sup〉5〈/sup〉 A/cm〈sup〉2〈/sup〉 at 10 K, 3T. 〈em〉J〈/em〉〈sub〉c〈/sub〉 performance of the 5 at% NaCl doped MgB〈sub〉2〈/sub〉 sample (NC05) reaches 6.8 × 10〈sup〉5〈/sup〉 A/cm〈sup〉2〈/sup〉 at 20 K, 2T, which improves approximately 20% compared to the pure one, attributing to the better grain connectivity of MgB〈sub〉2〈/sub〉 and enhancement of flux pinning force by NaCl doping.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 30 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 803〈/p〉 〈p〉Author(s): Yu Wang, Chao Fang, Xiang Li, Zhou Peng Li, Bin Hong Liu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉LaB〈sub〉6〈/sub〉 is a unique plasmonic material, for which the localized surface plasmon resonance (LSPR) absorption band intrinsically lies in the near infrared (NIR) region. In this work, we synthesized spherical LaB〈sub〉6〈/sub〉 nanoparticles with a tunable size within 50–200 nm. The optical properties of these LaB〈sub〉6〈/sub〉 nanospheres were found to be sensitive to the thickness of surface oxide layer that was formed during the synthesis, purification and dispersion processes. In order to enhance the stability of LaB〈sub〉6〈/sub〉 nanoparticles in aqueous environment, LaB〈sub〉6〈/sub〉@SiO〈sub〉2〈/sub〉 with a core-shell structure was successfully prepared. Both LaB〈sub〉6〈/sub〉 and LaB〈sub〉6〈/sub〉@SiO〈sub〉2〈/sub〉 demonstrated low cytotoxity in biomedical tests when their concentrations were limited to 0.2 mg mL〈sup〉−1〈/sup〉. The in vitro photothermal therapy experiment showed that 4T1 cancer cells were eventually apoptotic after being exposed to a 980 nm laser for 5 min at a considerably low power density of 0.82 W cm〈sup〉−2〈/sup〉 and a low dose of 0.1 mg mL〈sup〉−1〈/sup〉 for LaB〈sub〉6〈/sub〉@SiO〈sub〉2〈/sub〉. The results suggest that these LaB〈sub〉6〈/sub〉 nanospheres are viable photothermal agents for biomedical applications.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica, Volume 164〈/p〉 〈p〉Author(s): Siebo Reershemius, Mark Fittock, Troy L. Hudson, Kaname Sasaki, Marco Scharringhausen, Tilman Spohn, Tom Spröwitz, Torben Wippermann〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉On May 05, 2018 NASA JPL launched its mission to Mars called “InSight”. Main objective of this mission is to gain more knowledge of the evolution of terrestrial planets. Beside a number of different scientific instruments onboard the lander there are two instruments that will perform measurements on the Martian ground. One of the instruments is HP〈sup〉3〈/sup〉 (Heat Flow and Physical Properties Package), which was developed by the German Aerospace Center (DLR) to measure the heat flow of the Martian outer crust.〈/p〉 〈p〉Main elements of this instrument are the heat flow probe, the Backend Electronic and the Support System. With this paper the authors give a detailed insight of the function of the Support System within the instrument and its development.〈/p〉 〈p〉The Support System enables the operation of the heat flow probe on the surface. The mechanical design of the Support System is mainly driven by a unique set of requirements derived from the working environment on Mars, the deployment from the lander deck, and the mechanically separated operation on the surface. The paper will give an overview of the development and the qualification of the structure of the Support System. It will focus on the mechanical design and the analysis of the structural dynamics, and on the testing which includes standard environmental testing but also numerous development tests that are very mission specific.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 30 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 811〈/p〉 〈p〉Author(s): Miqi Wang, Zehua Zhou, Qijie Wang, Zehua Wang, Xin Zhang, Yuying Liu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉FeCrMoCBY amorphous coating with a high volume fraction of amorphous phase (90%) was prepared on Q235 steel by atmospheric plasma spraying. Influence of passivation potential on the corrosion resistance of passive films on the coating surface was estimated by electrochemical measurements, capacitance analysis, AFM and XPS technique. The results revealed that increasing potential promoted the growth of a more compact and thicker film due to the formation of more bounded water and oxides. Reduction in hydroxides further decreased point defects density significantly in the passive layer when passivated at a higher potential. A low diffusivity (1.67 × 10〈sup〉−15〈/sup〉 cm〈sup〉2〈/sup〉 s〈sup〉−1〈/sup〉) corresponding to point defects could suppress both the growth and degradation processes of passive film in chloride containing electrolyte, and thus enhance the film resistance to local thinning.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): Ahmed Gamal El-Shamy〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Novel conductive PVA/CQDs nanocomposite films were synthesized through the casting technique for the electromagnetic (EM) wave protection at microwave band. The surface morphology, thermal and mechanical properties were briefly studied. The SEM micrograph showed an excellent distribution, dispersion and a high adhesion property of the CQDs in the PVA chains. Also, DSC analysis showed an increase in the〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mtext〉glass〈/mtext〉〈mspace width="0.25em"〉〈/mspace〉〈mtext〉temperature〈/mtext〉〈mspace width="0.25em"〉〈/mspace〉〈mrow〉〈mo stretchy="true"〉(〈/mo〉〈msub〉〈mrow〉〈mi〉T〈/mi〉〈/mrow〉〈mrow〉〈mi〉g〈/mi〉〈mi〉l〈/mi〉〈mi〉a〈/mi〉〈mi〉s〈/mi〉〈mi〉s〈/mi〉〈/mrow〉〈/msub〉〈mo stretchy="true"〉)〈/mo〉〈/mrow〉〈/mrow〉〈/math〉 from 83.2 °C for fresh PVA to 95.4 °C for 8 wt% of CQD and the increase in melting temperature from 215 °C for fresh PVA to 227.7 °C for the same CQDs concentration. It was found that Young's modulus is directly proportional to CQD nano-particles concentration in the nano-composites from 0.14 GPa for fresh PVA to 4.48 GPa for 8 wt% of CQDs. It was found that the strength at break increases, but the elongation declines with the increase of CQDs nano-particles. The EM shielding effectiveness (SE) of (PVA/CQDs) nanocomposite is measured in the microwave frequency range, and it is found around 36.8 dB with the CQDs concentration (8 wt%). Finally, the PVA/CQDs nano-composite is of promising potential applications in electronics and microwave devices at an affordable cost.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925838819331846-fx1.jpg" width="148" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: Available online 20 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds〈/p〉 〈p〉Author(s): A. Rajabi, A.R. Mashreghi, S. Hasani〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this study, non-isothermal kinetic analysis of high temperature oxidation of Ti–6Al–4V alloy by thermogravimetric analysis (TGA) at heating rates of 10, 15, and 20 °C/min up to 1550 °C in air atmosphere was studied. The results revealed that the formed oxide layer consists of several different parts; an inner part of TiO〈sub〉2〈/sub〉, an outer part of TiVO〈sub〉4〈/sub〉, and an intermediate part of Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉. Also, the thickness of oxide layer increased by an increase in the maximum heating temperature, while its density decreased by formation of the pores and cracks in higher maximum temperature due to the mismatch between the thermal expansion coefficient of the oxide layer and the substrate. This mismatch led to formation of large stresses in the oxide layer at high temperatures (≥1000 °C) and thereby isolation of the oxide layer during cooling. The microhardness profiles shift to higher microhardness values by an increase in the maximum temperature due to the increasing of oxygen solubility in the substrate. On the other hand, the kinetic results performed by isoconversional Starink, KAS, FWO, Tang, and Friedman methods in combination with the invariant kinetic parameters (IKP) method and fitting model estimated the activation energy (〈em〉E〈/em〉) and pre-exponential factor (ln〈em〉A〈/em〉) of the oxidation process equal to 205–235 kJ/mol and 12-13 min〈sup〉−1〈/sup〉, respectively. Furthermore, it was approved that this reaction is controlled by a diffusion control model (D1 model).〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): Yuejun Chen, Shizhen Zhu, Yanqi Ji, Zhuang Ma, Hengyong Wei〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In order to avoid infrared emissivity deterioration of MoSi〈sub〉2〈/sub〉 particles result from its high-temperature oxidation, a satisfactory electrostatic self-assembly process was presented to synthesize MoSi〈sub〉2〈/sub〉@SiO〈sub〉2〈/sub〉 particles. A thermally stable and transmitting infrared SiO〈sub〉2〈/sub〉 shell was formed with tetraethyl orthosilicate (TEOS) as a precursor and tetrabutyl ammonium bromide (TBAB) as an electrostatic adsorbent after heat treatment at 1200 °C. The oxidation resistance, composition, micro-morphology and infrared emissivity of MoSi〈sub〉2〈/sub〉@SiO〈sub〉2〈/sub〉 were studied using thermogravimetric analysis, X-ray diffraction, energy disperse spectroscopy, scanning electron microscopy, and ultraviolet–visible near-IR spectrophotometer. The results demonstrated that MoSi〈sub〉2〈/sub〉 particle was thoroughly encapsulated by a SiO〈sub〉2〈/sub〉 glass shell, consequently, it exhibited great oxidation resistance compared with that of unencapsulated. More importantly, the emissivity of MoSi〈sub〉2〈/sub〉@SiO〈sub〉2〈/sub〉 particles had no obvious recession due to the intact encapsulation with TBAB. In addition, the electrostatic self-assembly mechanism of core-shell (MoSi〈sub〉2〈/sub〉@SiO〈sub〉2〈/sub〉) particles was discussed.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): Jingui Zong, Fei Wang, Guannan Liu, Mingshu Zhao, Sen Yang, Xiaoping Song〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Molybdenum disulfide (MoS〈sub〉2〈/sub〉), has aroused people's much research interest as an anode candidate for next generation of Li-ion batteries because of special layered structure and high theoretical capacity. However, MoS〈sub〉2〈/sub〉 suffers from a poor cycling stability and an inferior rate capability upon charge/discharge processes. So we have successfully synthesized a more stable expanded nanocomposite with superior electrical conductivity by intercalating moderate amorphous carbon between two adjacent S–Mo–S interlayer via a simple method which exhibits excellent lithium storage performance with high capacity (858.9 mA h g〈sup〉−1〈/sup〉 at 1 A g〈sup〉−1〈/sup〉 for 1000 cycles), and superior rate capability (518 mA h g〈sup〉−1〈/sup〉 at 4 A g〈sup〉−1〈/sup〉). This superior electrochemical performance is attributed to the special structure (few layers, 2H phase, expanded interlayer spacing, amorphous carbon between S–Mo–S layers, C–O–Mo bond in the layer), small size and evenly distributed MoS〈sub〉2〈/sub〉 nanosheets. Besides, we study the 2H-1T phase transformation mechanism by controlling the ratio of ethylene glycol to water and O–C〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/dbnd"〉O bond plays an important role in promoting 2H-1T phase transformation.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): Qinjiang He, Renli Fu, Xiufeng Song, Haitao Zhu, Xinqing Su, Chaoqun You〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Herein, Ce〈sup〉3+〈/sup〉 and Ce〈sup〉3+〈/sup〉/Dy〈sup〉3+〈/sup〉 co-doped Ca〈sub〉3〈/sub〉Al〈sub〉2〈/sub〉O〈sub〉6〈/sub〉 phosphors have been designed and synthesized via a facile citrate-based sol-gel technique, and their structural, photoluminescence properties and energy transfer phenomenon were investigated comprehensively. The XRD analysis indicated that pure Ca〈sub〉3〈/sub〉Al〈sub〉2〈/sub〉O〈sub〉6〈/sub〉 phase can be synthesized at low temperature (1000 °C) for merely 2 h. The photoluminescence spectra showed the dominant emission of Ce〈sup〉3+〈/sup〉 singly doped phosphors is located in the blue region even at low Ce〈sup〉3+〈/sup〉 doping level, which indeed favors the energy transfer from Ce〈sup〉3+〈/sup〉 to other luminescent centers. When Dy〈sup〉3+〈/sup〉 is co-doped into Ca〈sub〉3〈/sub〉Al〈sub〉2〈/sub〉O〈sub〉6〈/sub〉:Ce〈sup〉3+〈/sup〉 phosphors, the remarkable sensitizing effect of Ce〈sup〉3+〈/sup〉 on Dy〈sup〉3+〈/sup〉 is validated by comparatively analyzing the excitation, emission spectra and average lifetimes of the series of samples. Through the concentration quenching theory, the critical distance between Ce〈sup〉3+〈/sup〉 and Dy〈sup〉3+〈/sup〉 is calculated to be 13.50 Å. Furthermore, the energy transfer mechanism between them is most likely ascribed to electric dipole-dipole interaction. In virtue of the variation of the emission intensities of Ce〈sup〉3+〈/sup〉 and Dy〈sup〉3+〈/sup〉, the emitting colors of Ca〈sub〉3〈/sub〉Al〈sub〉2〈/sub〉O〈sub〉6〈/sub〉:Ce〈sup〉3+〈/sup〉, Dy〈sup〉3+〈/sup〉 phosphors can realize tunable luminescence from deep blue to bluish-white region through controlling the Dy〈sup〉3+〈/sup〉 content. Based on these analysis, Ca〈sub〉3〈/sub〉Al〈sub〉2〈/sub〉O〈sub〉6〈/sub〉:Ce〈sup〉3+〈/sup〉, Dy〈sup〉3+〈/sup〉 phosphors could potentially be applied as a single-phase color-tunable phosphors pumped by near-ultraviolet (n-UV) radiation.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): Zhaohui Ma, Jiandong Zhang, Guoqing Yan, Hai Liu, Jingcun Huang, Lijun Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Thermodynamic properties of zirconium-oxygen (Zr–O) solid solution and its deoxidation by calcium in CaCl〈sub〉2〈/sub〉 molten salt were studied using a chemical equilibration technique. In the temperature range from 1173 to 1373 K, the equilibrium oxygen contents in Zr were measured experimentally under coexistence of Ca and CaO in CaCl〈sub〉2〈/sub〉 molten salt. The oxygen content in Zr was reduced from about 800 ppm to a minimum of less than 100 ppm. Then 〈em〉a〈/em〉〈sub〉CaO〈/sub〉 sensor — niobium-oxygen (Nb–O) solid solution was employed to equilibrate with Zr–O solid solution to determine the oxygen activity coefficient in Zr–O solid solution. Zr and Nb specimens were submerged in Ca-saturated CaCl〈sub〉2〈/sub〉 molten salt containing different amounts of CaO. CaCl〈sub〉2〈/sub〉 melt was used for a homogeneous reaction and composition. The experimental results shown that Henry's law held and the activity coefficient of oxygen was constant within the concentration range of this study. Based on the result, the standard formation Gibbs free energy of Zr–O solid solution was obtained as a function of temperature:〈span〉〈span〉1/2O〈sub〉2〈/sub〉 (g) = O (in Zr)〈/span〉〈/span〉〈span〉〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si17.svg"〉〈mrow〉〈mi〉Δ〈/mi〉〈msubsup〉〈mi〉G〈/mi〉〈mrow〉〈mi〉Z〈/mi〉〈mi〉r〈/mi〉〈mo linebreak="badbreak"〉−〈/mo〉〈mi〉O〈/mi〉〈/mrow〉〈mi〉θ〈/mi〉〈/msubsup〉〈mo linebreak="badbreak"〉=〈/mo〉〈mo linebreak="goodbreak"〉−〈/mo〉〈mn〉543577〈/mn〉〈mo linebreak="goodbreak"〉+〈/mo〉〈mn〉64〈/mn〉〈mtext〉.〈/mtext〉〈mn〉3〈/mn〉〈mi mathvariant="italic"〉T〈/mi〉〈mrow〉〈mo〉(〈/mo〉〈mtext〉1173−1373K〈/mtext〉〈mo〉)〈/mo〉〈/mrow〉〈/mrow〉〈/math〉〈/span〉〈/p〉 〈p〉The 〈em〉p-t-x〈/em〉 relationship of the deoxidation system was obtained simultaneously, which make the deoxidation limit and variation trend of oxygen content in Zr–O solid solution predictable and controllable under different conditions. Oxygen distribution coefficient between Zr–O solid solution and Nb–O solid solution was found in agreement with the theoretical value and independent of oxygen potential of the system.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): Liang Ma, Shu-Shen Lyu, Yao Dai, Xian-Yinan Pei, Dong-Chuan Mo, Yuan-Xiang Fu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Transition metal oxide/reduced graphene oxide (TMO/RGO) composites have been explored for development as anode materials for lithium-ion batteries (LIBs); TMOs have high theoretical capacities, and the oxidation degrees of RGO sheets can directly affect the lithium storage performance of TMO/RGO composites. In this work, several NiO/reduced graphene oxide composites (NiO/RGO) are prepared based on oxidation degrees of graphite oxide sheets (GOs) through an ultrasonic agitation method. These composites are then explored as anodes for LIBs. Results show that the reversible capacity of NiO/RGO composites increases gradually to 1046 mA h/g and then declines to 956 mA h/g after 50 cycles at 100 mA/g. The variation rule of lithium storage properties of NiO/RGO samples can be attributed to the surface functional groups of RGO sheets, which can affect interfacial interaction between NiO and RGO sheets due to the different oxidation degrees of GO. Different RGO sheets also show distinct abilities to hinder NiO pulverisation and promote lithium-ion/electron diffusion during repeated charge and discharge processes.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 20 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds〈/p〉 〈p〉Author(s): Kaixuan Chen, Shiwei Pan, Xiaohua Chen, Zidong Wang, Rolf Sandström〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The microstructure evolution in the as-cast pure Cu and Cu-(1.0–3.0)Fe-0.5Co and Cu-1.5Fe-0.1Sn (wt. %) alloys was characterised in the previous work. Herein, the plastic deformation characteristics were examined by uniaxial tensile tests at room temperature. Along with the microstructure evolution, the yield strength increased with increasing Fe content and reached a peak value at 1.5 wt % Fe, but thereafter decreased with the further addition of Fe in the Cu–Fe–Co alloys. Nevertheless, the tensile strength and elongation synchronously improve with increasing Fe content. In particular, the Cu-1.5Fe-0.1Sn alloy achieved the optimal strength–ductility combination. In terms of the strengthening mechanism, the (Fe, Co)- or (Fe, Sn)-doped copper encouraged impediment, trapping, and storage of dislocations by the iron-rich nanoparticles and grain boundaries, which enhanced the strength and sustained the work hardening and elongation. The evolution of mechanical properties under an alloying effect was quantitatively described by the strengthening models. The results indicate that the optimum balance between strength and ductility was achieved by designing a microstructure containing fine grains, intragranular smaller spherical nanoparticles, and a minor solute element with higher misfit and higher growth restriction effect. The necessities for engineering a microstructure to achieve simultaneously strong and ductile bulk metals were discussed.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925838819331500-fx1.jpg" width="443" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): Natalia Pawlik, Barbara Szpikowska-Sroka, Tomasz Goryczka, Wojciech A. Pisarski〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In the present paper, the nanocrystalline transparent oxyfluoride SrF〈sub〉2〈/sub〉:Eu〈sup〉3+〈/sup〉 glass-ceramic materials (nGCs) were synthesized via a low-temperature sol-gel method, in which trifluoroacetic acid (TFA) was used as a fluorination reagent. The thermal degradation of precursor xerogels was examined by TG/DSC analysis and the formation of SrF〈sub〉2〈/sub〉 nanocrystals inside silicate xerogel host was proved by XRD measurements. Additionally, to verify the structural changes within silicate network during ceramization process, the IR-ATR measurements were also carried out. The optical properties of Eu〈sup〉3+〈/sup〉 ions in precursor xerogels and fabricated nGCs were investigated based on photoluminescence excitation (PLE: λ〈sub〉em〈/sub〉 = 611 nm) and emission (PL: λ〈sub〉exc〈/sub〉 = 393 nm) spectra as well as luminescence decay analysis of the 〈sup〉5〈/sup〉D〈sub〉0〈/sub〉 excited level. It was observed, that for precursor silica xerogels the electric-dipole transition (ED) 〈sup〉5〈/sup〉D〈sub〉0〈/sub〉 → 〈sup〉7〈/sup〉F〈sub〉2〈/sub〉 was dominant, meanwhile the magnetic-dipole transition (MD) 〈sup〉5〈/sup〉D〈sub〉0〈/sub〉 → 〈sup〉7〈/sup〉F〈sub〉1〈/sub〉 had the greatest intensity for SrF〈sub〉2〈/sub〉:Eu〈sup〉3+〈/sup〉 nGCs. Thus, the R/O-ratio (R/O = I(〈sup〉5〈/sup〉D〈sub〉0〈/sub〉 → 〈sup〉7〈/sup〉F〈sub〉2〈/sub〉)/I(〈sup〉5〈/sup〉D〈sub〉0〈/sub〉 → 〈sup〉7〈/sup〉F〈sub〉1〈/sub〉)) was calculated to estimate the symmetry in the local framework around Eu〈sup〉3+〈/sup〉 ions. Moreover, the reddish-orange photoluminescence is long-lived (about 30-fold longer) for SrF〈sub〉2〈/sub〉:Eu〈sup〉3+〈/sup〉 nGCs compared with xerogels. The changes in emission spectra as well as double-exponential character of luminescence decay curves recorded for obtained nGCs indicated the successful migration of optically active Eu〈sup〉3+〈/sup〉 ions from amorphous silica framework to low phonon energy SrF〈sub〉2〈/sub〉 nanocrystal phase.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 21 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds〈/p〉 〈p〉Author(s): Ping Song, Wen-bin Li, Yu Zheng, Zhong-wei Guan, Xiao-ming Wang, Wen-xu Xu, Peng Ge〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The compressive and tensile stress–strain relationship and fracture behavior of a new low-cost titanium alloy Ti–5Al–3V–2Cr–2Fe (Ti–5322) at 286–573 K, a strain rate of 0.0001–4300 s〈sup〉−1〈/sup〉 and a stress triaxiality of 0.43–1.6 were studied. Based on the experimental data, the flow and fracture behavior of Ti–5322 was established based on the Johnson–Cook (J–C) equation. Ballistic impact tests were used to study the ballistic performance of a 7-mm-thick Ti–5322 target and the accuracy of the constitutive model was verified from the ballistic test results. The experimental results showed that the yield strength and strain rate of the Ti–5322 were related logarithmically. As the strain rate increased, the rate-strengthening behavior of the material weakened gradually. The material had an obvious thermal-softening behavior and the yield strength decreased linearly with an increase in deformation temperature. The stress triaxiality and strain rate had a significant effect on the fracture behavior of Ti–5322. The material fracture strain decreased with the stress triaxiality and an increase in strain rate. The J–C constitutive model was a good predictor for the ultimate penetration velocity of the Ti–5322 target and the velocity decay of fragments during penetration. The ballistic limit velocity of the 10-mm-diameter tungsten-alloy ball to the 7-mm-thick Ti–5322 target at 0° and 30° was 416.0 m/s and 484.8 m/s, respectively.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): Dongqing Liu, Yimin Yin, Haifeng Cheng〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Transient memristor is highly desirable for secure memory system and secure neuromorphic computing. Here, a transient memristor with the MgO thin film as resistive dielectric material and the Ni as electrode material is reported. The memristor shows reversible and nonvolatile bipolar resistive switching performance, narrow distribution of low resistance state (LRS) and high resistance state (HRS), uniform switching voltages and stable retention at room temperature. It is indicated that the resistive switching mechanism of the memristor is conductive filament in LRS and space charge limiting current in HRS. In addition, the memristor can be failed after immersed in deionized water for 5 min due to the film damage resulting from large frizzle and the dissolution of Ni and MgO film. The prepared memristor has potential for secure memory system application.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): Lei Zhang, Shan Ji, Rongfang Wang, Dan J.L. Brett, Hui Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A flexible cathode with highly electrochemical performance for bendable supercapacitors have been achieved by electrochemical depositing hierarchical nanostructured Ni〈sub〉3〈/sub〉S〈sub〉2〈/sub〉/Ni(OH)〈sub〉2〈/sub〉 compounds on the surface of commercial conductive textile. The morphology and physical properties of as-prepared electrode are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS). Based on its unique nanostructure, the obtained flexible Ni〈sub〉3〈/sub〉S〈sub〉2〈/sub〉/Ni(OH)〈sub〉2〈/sub〉 electrode exhibits a highly electrochemical capacitance of 1800 F g〈sup〉−1〈/sup〉 at 3 mA cm〈sup〉−2〈/sup〉 with good rate capability, excellent stability and bendability. Ni〈sub〉3〈/sub〉S〈sub〉2〈/sub〉/Ni(OH)〈sub〉2〈/sub〉 electrode as cathode is assembled with active carbon as anode and PVA/KOH as electrolyte into an asymmetric capacitor to evaluate its performance in a real supercapacitor. The obtained supercapacitor cell delivers a high energy density of 0.49 mWh cm〈sup〉−2〈/sup〉 at 3.54 mW cm〈sup〉−2〈/sup〉 and maintains the energy density at 0.38 Wh cm〈sup〉−2〈/sup〉 when power density increases to 21.53 mW cm〈sup〉−2〈/sup〉. When the assembled cells are connected in series, these connected cells can work safely and properly at a much higher voltage window due to their good stability and consistency. Considering its low-cost, facile fabrication and highly electrochemical performance, the obtained Ni〈sub〉3〈/sub〉S〈sub〉2〈/sub〉/Ni(OH)〈sub〉2〈/sub〉 electrode is a promising flexible material.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S092583881933110X-fx1.jpg" width="255" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): Runchen Jia, Weidong Zeng, Shengtong He, Xiongxiong Gao, Jianwei Xu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Fracture toughness and fracture mechanism of Ti60 alloy with duplex microstructure under different temperature conditions were investigated in the present work. The experimental result shows that the fracture toughness of CT samples increases from the room temperature (40  MPa m〈sup〉1/2〈/sup〉) to 400 °C (71.45  MPa m〈sup〉1/2〈/sup〉) but declines at 600 °C (62.55  MPa m〈sup〉1/2〈/sup〉). It is observed from fracture surface through SEM that the predominant fracture mechanism has changed from quasi-cleavage fracture at room temperature to ductile fracture at higher temperatures. In addition, the tortuosity of crack propagation path has a limited impact on the fracture toughness. Path selections for crack propagation are obtained through SEM observation which can be summarized as: cut through lamellar 〈em〉α〈/em〉, parallel to lamellar 〈em〉α〈/em〉, bypass the equiaxed 〈em〉α〈/em〉〈sub〉〈em〉p〈/em〉〈/sub〉 and cut through the equiaxed 〈em〉α〈/em〉〈sub〉〈em〉p〈/em〉〈/sub〉. Moreover, it is found that the intrinsic contribution is the primary reason leading to the change of the fracture toughness of Ti60 alloy under different temperatures. Meanwhile, it is noteworthy that the area of the crack tip plastic zone increases from RT to 400 °C but decreases at 600 °C, which is seen as the main impact of temperature on fracture toughness. To be exact, the CT sample with a larger area of the plastic zone could provide a higher 〈em〉K〈/em〉〈sub〉〈em〉1C〈/em〉〈/sub〉 value. Furthermore, a prediction model of 〈em〉K〈/em〉〈sub〉〈em〉1C〈/em〉〈/sub〉 based on tensile properties is established, which has a good accuracy with experimental results. The model is useful in predicting the fracture toughness of Ti60 alloy at different test temperatures.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): Shuying Dong, Longji Xia, Fangyuan Zhang, Fengzi Li, Yuyao Wang, Lingfang Cui, Jinglan Feng, Jianhui Sun〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The ZnSn(OH)〈sub〉6〈/sub〉 nanocubes were prepared under different pH (3–12.4) by liquid precipitation, well characterized and further used for wastewater treatment. The results indicated that the ZnSn(OH)〈sub〉6〈/sub〉 nanocubes prepared at pH = 11.1 possessed of uniform size distribution and excellent photocatalytic activity, the degradation efficiency to MB reaches 76.3% after 5 h natural sunlight irradiation. Subsequently, the prepared ZnSn(OH)〈sub〉6〈/sub〉 nanocubes was further thermal treated (200 °C, 24 h) in four different solvents, containing deionized water, stock solution, mixed solution (V〈sub〉water〈/sub〉: V〈sub〉ethanol〈/sub〉: V〈sub〉glacial acetic acid〈/sub〉 = 3:1:1) and ethanol, named as H-1, H-2, H-3 and H-4, respectively. H-2 and H-3 showed superior photocatalytic performance and the removal efficiency of MB improved to be almost 100%, as well as red-shifted light absorption edge and the band gap energies reduced 0.9 and 0.93 eV, respectively. Moreover, free radical capture experiments showed that the h〈sup〉+〈/sup〉 and ·O〈sub〉2〈/sub〉〈sup〉−〈/sup〉 are the main active species for the ZnSn(OH)〈sub〉6〈/sub〉 nanocubes and H-2, respectively, while all these three ·OH, ·O〈sub〉2〈/sub〉〈sup〉−〈/sup〉 and 〈sup〉1〈/sup〉O〈sub〉2〈/sub〉 radicals for H-3. Those results suggested that both pH regulation and thermal treatment could efficiently improve the microscopic morphology, crystal structure and photocatalytic activity of the ZnSn(OH)〈sub〉6〈/sub〉, which might pave the way for the artful design of other high-performance catalysts.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925838819332013-fx1.jpg" width="312" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica, Volume 164〈/p〉 〈p〉Author(s): A.K. de Almeida, A.F. Bertachini de Almeida Prado, R. Vilhena de Moraes, M. Lara〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Integral indices are useful tools to be used to identify characteristics of an orbit. Using analytical solutions for a perturbative version of the Tsien problem (radial low thrust applied to a spacecraft), two indices are defined and evaluated. They can make a map of the orbits disturbed by the thrust.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 22 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica〈/p〉 〈p〉Author(s): Yoji Ishikawa, Yasuhiro Fuchita, Takashi Hitomi, Yoku Inoue, Motoyuki Karita, Kohei Hayashi, Takayuki Nakano, Naoko Baba〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Carbon nanotube (CNT) yarns were exposed to the space environment on the international space station (ISS) at low Earth orbit (LEO) of around 400 km altitude. Ground-based comparison tests, including irradiation of atomic oxygen (AO), electron beam (EB) and ultraviolet (UV) individually for different sets of samples, were performed. Significant deterioration of the outer surface and substantial reduction in tensile strength were found for AO irradiated CNT yarns among the ground-based comparison tests. Transmission electron microscopic observation revealed that crystal structure of CNT was physically damaged showing sharp graphene edges. As to the space exposure tests, quite similar damages and decrease in tensile strength were observed on the CNT yarns. We found that high kinetic energy impacts of the AO at LEO cause severe damages on carbon crystal materials.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): Dongdong Zhang, Qiang Yang, Kai Guan, Baishun Li, Nan Wang, Pengfei Qin, Bo Jiang, Chi Sun, Xin Qin, Zheng Tian, Zhanyi Cao, Jian Meng〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A high-strength low-rare-earth-alloyed Mg−3.5Sm−2Yb−0.6Zn−0.4Zr alloy was processed by an ingot metallurgy process with hot-extrusion followed by artificial aging. The peak-aged sample exhibited a higher yield strength of 449 MPa than most of extruded Mg−Gd based alloy containing high RE content, and even is comparable to that of the T8-treated 2024 Al alloy. The studied alloy exhibited a typical bimodal microstructure, consisting of dynamically recrystallized (DRXed) grains with random textures and coarse unrecrystallized regions with strong basal fiber texture. In addition, the fragmented Mg〈sub〉5〈/sub〉RE and Mg〈sub〉41〈/sub〉RE〈sub〉5〈/sub〉 phases distributed at extrusion stringers. Abundant of fine Mg〈sub〉3〈/sub〉RE particles precipitated dynamically in DXRed regions, which restrains DRXed grains growth effectively by grain boundary pinning. Within the unDXRed regions, uniformly dense Mg〈sub〉3〈/sub〉RE and Mg〈sub〉12〈/sub〉RE nano-precipitates were observed. Also there were many basal 〈〈strong〉a〈/strong〉〉 dislocations and a few non-basal 〈〈strong〉c〈/strong〉 + 〈strong〉a〈/strong〉〉 dislocations in unDXRed regions. Subsequent artificial ageing significantly enhanced the alloy's strength by introducing basal precipitates, although decreased the ductility slightly. Finally, the ultrahigh yield strength was revealed to be attributed to the combined effects of a strong basal fiber texture, a bimodal microstructure, and numerous precipitated particles.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 22 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds〈/p〉 〈p〉Author(s): Sunil Chauhan, Manoj Kumar, Himanshu Pandey, Sandeep Chhoker, S.C. Katyal〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Ca and Ca–Li substitution dependent modification in structural, electron density, vibrational, magnetic and optical properties of BiFeO〈sub〉3〈/sub〉 nanoparticles synthesized by tartaric acid based sol–gel route are reported. X-ray diffraction and transmission electron microscopy techniques revealed the phase purity and nanocrystalline nature of BiFeO〈sub〉3〈/sub〉, Bi〈sub〉0·95〈/sub〉Ca〈sub〉0·05〈/sub〉FeO〈sub〉3〈/sub〉, Bi〈sub〉0·95〈/sub〉Ca〈sub〉0·05〈/sub〉Fe〈sub〉0·95〈/sub〉Li〈sub〉0·05〈/sub〉O〈sub〉3〈/sub〉 samples. The electron density plots indicated the displacement of Bi and Fe ions and partial covalency of Bi–O and Fe–O the bonds. The Ca and Ca–Li ions substitution induced distortion in rhombohedral structure resulting in enhanced magnetization of BiFeO〈sub〉3〈/sub〉 nanoparticles. The magnetization is highest for Ca–Li substituted BiFeO〈sub〉3〈/sub〉 nanoparticles with saturation magnetization of 0.036 emu/g due to the canted spin structure and uncompensated surface spins. The enhanced magnetic properties are also endorsed by the electron spin resonance and Raman studies. The band-gap of BiFeO〈sub〉3〈/sub〉 nanoparticles can be tuned by aliovalent ions substitution from 2.26 eV for BiFeO〈sub〉3〈/sub〉 to 2.20 and 2.17 eV for Ca, and Ca–Li substituted BiFeO〈sub〉3〈/sub〉 nanoparticles respectively.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): Lifeng Sun, Junjie Shi, Chengjun Liu, Maofa Jiang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉With the purpose of providing fundamental understanding of equilibrium phase relations with the addition of Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 to CaO–SiO〈sub〉2〈/sub〉-5wt%MgO–Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉–TiO〈sub〉2〈/sub〉 system, the equilibria phase relations were experimental determined from 1300 °C to 1450 °C at constant 〈em〉w〈/em〉(CaO)/〈em〉w〈/em〉(SiO〈sub〉2〈/sub〉) ratio of 1.50 using high temperature equilibrium and quenching method followed by XRD (X-Ray diffraction) and SEM-EDX (Scanning Electron Microscope and Energy Dispersive X-ray Fluorescence scope) analysis. The results showed that with the increase of Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 content up to 30 wt%, the coexisting equilibria solid phases gradually changed from perovskite of CaO·TiO〈sub〉2〈/sub〉 and melilite solid solution of (2CaO·Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉·SiO〈sub〉2〈/sub〉, 2CaO·MgO·2SiO〈sub〉2〈/sub〉)〈sub〉ss〈/sub〉 to spinel of MgO·Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉. Comparisons with the predictions by Factsage revealed that the simulated results were only well agreed when Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 content lower than 20 wt%, while significant discrepancies existed with Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 content higher than 30 wt%. Finally, the 1400 °C and 1450 °C isotherms, as well as the predicted primary phase boundary lines were projected on the pseudo-ternary phase diagram of CaO–SiO〈sub〉2〈/sub〉-5wt.%MgO–Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉–TiO〈sub〉2〈/sub〉 system within specific composition range.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): Mustafa A. Ahmed, Liza Coetsee, Walter E. Meyer, Jackie M. Nel〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Schottky diodes based on ZnO nanorods, undoped and co-doped with different concentrations (0.0, 0.2, 0.4, 0.6 and 0.8 at.%) of Ce and Sm, were fabricated on glass and on n-Si (111) substrates using chemical bath deposition assisted with the sol-gel spin coating. The ZnO maintained its hexagonal shape up to higher levels of doping (0.8 at.%) with the growth rate being suppressed by Ce and Sm co-doping. The as-synthesized nanorods were found to be highly crystalline and no impurities or peaks related to Ce and Sm or their oxides were observed. Room temperature Raman spectroscopy revealed that the prominent E〈sub〉2〈/sub〉 high peak shifted towards a lower wave number and the intensity decreased upon doping. X-ray photoelectron spectroscopy studies at room temperature showed that the presence of Zn and O in all samples with small amounts of Ce and Sm being detected at doping levels of 0.8 at.%. Photoluminescence studies at room temperature revealed a weak ultraviolet emission and a strong deep level (visible) emission. Deconvolution of the visible emission spectra showed that more than one defect contributed to the visible emission. The 〈em〉I–V〈/em〉 characteristics of the fabricated Schottky diode devices measured at room temperature showed that the Ce and Sm co-doping increased the generation-recombination process in the fabricated Schottky diodes. Furthermore, the current transport mechanism in the fabricated Schottky devices at a lower voltage (0.0–〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mo〉∼〈/mo〉〈/mrow〉〈/math〉 0.6 V) was dominated by ohmic conduction mechanism, while at voltages greater than 0.6 V, the space charge limited current and the trap filled limit voltage mechanism dominated.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): Ling Guo, Liyun Cao, Jianfeng Huang, Yong Wang, Wenbin Li, Hui Qi, Shaoyi Chen, Jiayin Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Owing to the high theoretical capacity, Sb〈sub〉2〈/sub〉Se〈sub〉3〈/sub〉 has been regarded as one of the best choices for Sodium-ion batteries (SIBs) anode materials. However, Sb〈sub〉2〈/sub〉Se〈sub〉3〈/sub〉 anode suffers from huge volume change with poor electrode structure stability, resulting in limited cycling and rate performance. Herein, inspired by the formation of inclusion complex an effective strategy for improving unstable molecules in biological fields, we encapsulate Sb〈sub〉2〈/sub〉Se〈sub〉3〈/sub〉 in capsular carbon shell via a hydrothermal and calcinations process. Furthermore, by adjusting the thickness of the capsule carbon shell, an ultra-stable Sb〈sub〉2〈/sub〉Se〈sub〉3〈/sub〉 electrode structure is realized. Equipped with this ultra-stable electrode structure, Sb〈sub〉2〈/sub〉Se〈sub〉3〈/sub〉 anode exhibits high capacity of 475 mA h g〈sup〉−1〈/sup〉 at 2 A g〈sup〉−1〈/sup〉 even after 600 cycles, showing compelling advantage on Na storage performance compared to other reported Sb-based anode materials. The analysis results indicate that the intact capsular carbon shell can effectively remit huge volume change of Sb〈sub〉2〈/sub〉Se〈sub〉3〈/sub〉, and act like a reaction vessel in which the sodiation/desodiation reaction of Sb〈sub〉2〈/sub〉Se〈sub〉3〈/sub〉 is carried out regularly. Therefore, this ultra-stable electrode provides stable redox reactions, easy charge transfer and fast sodium ion diffusion, resulting in excellent Na storage performance of Sb〈sub〉2〈/sub〉Se〈sub〉3〈/sub〉 anode.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉Encapsulating Sb〈sub〉2〈/sub〉Se〈sub〉3〈/sub〉 in capsular carbon shell to from inclusion complex can achieve ultra-stable electrode structure with excellent Na storage performance.〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925838819331706-fx1.jpg" width="466" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: Available online 22 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica〈/p〉 〈p〉Author(s): D.K. Bond, B. Goddard, R.C. Singleterry, S. Bilbao y Leóna〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Materials have a primary purpose in the design of space vehicles, such as fuels, walls, racks, windows, etc. Additionally, each will also affect space radiation protection. The shielding capabilities of 59 materials are evaluated for deep space travel, in terms of whole body effective dose equivalent and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mfrac〉〈mrow〉〈mo〉#〈/mo〉〈mtext〉 〈/mtext〉〈mi〉o〈/mi〉〈mi〉f〈/mi〉〈mtext〉 〈/mtext〉〈mi〉N〈/mi〉〈mi〉u〈/mi〉〈mi〉c〈/mi〉〈mi〉l〈/mi〉〈mi〉e〈/mi〉〈mi〉o〈/mi〉〈mi〉n〈/mi〉〈mi〉s〈/mi〉〈/mrow〉〈mrow〉〈mi〉V〈/mi〉〈mi〉o〈/mi〉〈mi〉l〈/mi〉〈mi〉u〈/mi〉〈mi〉m〈/mi〉〈mi〉e〈/mi〉〈/mrow〉〈/mfrac〉〈/mrow〉〈/math〉. The hydrogen rich materials were evaluated further using 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.svg"〉〈mrow〉〈mfrac〉〈mrow〉〈mo〉#〈/mo〉〈mtext〉 〈/mtext〉〈mi〉o〈/mi〉〈mi〉f〈/mi〉〈mtext〉 〈/mtext〉〈mi〉H〈/mi〉〈mi〉y〈/mi〉〈mi〉d〈/mi〉〈mi〉r〈/mi〉〈mi〉o〈/mi〉〈mi〉g〈/mi〉〈mi〉e〈/mi〉〈mi〉n〈/mi〉〈mtext〉 〈/mtext〉〈mi〉A〈/mi〉〈mi〉t〈/mi〉〈mi〉o〈/mi〉〈mi〉m〈/mi〉〈mi〉s〈/mi〉〈/mrow〉〈mrow〉〈mi〉M〈/mi〉〈mi〉a〈/mi〉〈mi〉s〈/mi〉〈mi〉s〈/mi〉〈/mrow〉〈/mfrac〉〈/mrow〉〈/math〉 and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.svg"〉〈mrow〉〈mfrac〉〈mrow〉〈mo〉#〈/mo〉〈mtext〉 〈/mtext〉〈mi〉o〈/mi〉〈mi〉f〈/mi〉〈mtext〉 〈/mtext〉〈mi〉H〈/mi〉〈mi〉y〈/mi〉〈mi〉d〈/mi〉〈mi〉r〈/mi〉〈mi〉o〈/mi〉〈mi〉g〈/mi〉〈mi〉e〈/mi〉〈mi〉n〈/mi〉〈mtext〉 〈/mtext〉〈mi〉A〈/mi〉〈mi〉t〈/mi〉〈mi〉o〈/mi〉〈mi〉m〈/mi〉〈mi〉s〈/mi〉〈/mrow〉〈mrow〉〈mi〉V〈/mi〉〈mi〉o〈/mi〉〈mi〉l〈/mi〉〈mi〉u〈/mi〉〈mi〉m〈/mi〉〈mi〉e〈/mi〉〈/mrow〉〈/mfrac〉〈/mrow〉〈/math〉. All evaluated materials, through density, composition, and shielding ability, can be categorized into three groups: metals, polymers and composites, and fuels, hydrides, and liquid gases. The analyses presented in the article shows that a “magic” material is not possible; however polymers and composites should be used instead of metals, if they can serve their primary purpose. Polyethylene and magnesium borohydride are shown to be the best feasible materials from this sample. Thermal neutron absorbers, 〈sup〉6〈/sup〉Li and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.svg"〉〈mrow〉〈mmultiscripts〉〈mn〉0〈/mn〉〈mprescripts〉〈/mprescripts〉〈none〉〈/none〉〈mn〉1〈/mn〉〈/mmultiscripts〉〈/mrow〉〈/math〉B, do not have a significant effect on 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si5.svg"〉〈mrow〉〈msub〉〈mi〉E〈/mi〉〈mi〉D〈/mi〉〈/msub〉〈/mrow〉〈/math〉. Alloying of materials, such as aluminum, for strengthening purposes, do not increase 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si5.svg"〉〈mrow〉〈msub〉〈mi〉E〈/mi〉〈mi〉D〈/mi〉〈/msub〉〈/mrow〉〈/math〉. Ultimately, a space vehicle is a system of systems and radiation protection must be one of them.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 21 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica〈/p〉 〈p〉Author(s): Xiaolong Yang, Zhijun Wei, Zelin Zhang, Jingjia Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Due to great demands on solid rocket motors and solid ramjets for thrust control, a study of the effect of high-voltage electric fields on the regression rate of polymethyl methacrylate (PMMA) has been undertaken. The flame shape was recorded by a CMOS camera. The regression rate of PMMA was measured. A numerical model of fluid-solid coupling, which is based on experiment and considers physico-chemical phenomena associated with the flame-field interaction process, has been developed to explain experimental observations. In order to reduce the computational workload, the radiation loss, including the soot radiation is not considered in the numerical simulation. The mechanism of the effect of electric fields on the regression rate of PMMA is analysed. The numerical simulation shows that the change of the regression rate of a PMMA tip under the action of electric fields is consistent with experimental results. Studies show that electric fields can change the regression rate of PMMA, increasing it by about 38%. The regression rate on the burning surface is increased when subjected to positive electric fields. Under a negative electric field, part of the burning surface is subjected to an increased regression rate, and some thereof is subjected to a decreased regression rate. The effect of electric fields on the regression rate of PMMA is mainly due to the interaction of buoyancy and the electric field induced volumetric body forces.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica, Volume 164〈/p〉 〈p〉Author(s): S. Khoroshylov〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉According to the concept of active debris removal, named “ion beam shepherd”, a shepherd satellite must be controlled to move at a certain small distance in front of a space debris object during the de-orbiting phase. Due to the considerable duration of this phase, the propellant consumption is a key driver for the control system design. As shown in recent studies, the in-plane relative motion of such a formation can be controlled using a thrust variation of only one compensation thruster of the shepherd. This control strategy allows designers to significantly reduce the propellant mass needed to fulfill a de-orbiting mission but does not ensure the controllability of the formation in the out-of-plane direction. To fill this gap this paper proposes to deviate the yaw attitude of the shepherd for applying control actions in the out-of-plane direction. The laws of the yaw angle variation are designed to effectively damp out the out-of-plane oscillations. Computer simulations demonstrate that a required relative spatial position of the formation can be maintained by varying only two values: the yaw angle of the shepherd and thrust of the compensation thruster. The analysis shows that the de-orbiting rate deteriorates insignificantly due to the attitude deviation of the ion beam.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 21 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica〈/p〉 〈p〉Author(s): Mingjian Wu, Zhiwei Shi, Tianhang Xiao, Z.L.J. Chen, Haisong Ang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The parameters of solar cell efficiency, flight date of year, latitude and sun elevation angle are important to energy conversion of solar cells, which affect optimal flight control and energy performance of Z-shaped solar aircraft. This work is mainly focusing on studying the effect of varying these parameters on optimum attitude planning, optimum wing morphing control and maximum net energy input for Z-shaped solar aircraft. This study shows that, with higher solar cell efficiency, the solar aircraft prefers to more daylight hours configured as Z-shaped wing, larger morphing angle and larger angle between projection of sunlight and wingspan axis, which enhances to achieve more net power input. For the middle and high latitudes in winter with low sun elevation angles, the Z-shaped solar aircraft tends to large morphing angles and small angles between projection of sunlight and wingspan axis. For the low and middle latitudes of the other seasons with high sun elevation angles, it prefers to small morphing angles to make its central wing totally expose to the sunlight, and orient flight attitude to make the projection of sunlight coincide with wingspan axis. Moreover, the research on the impact of solar cell efficiency shows that, compared with the planar wing, the optimal Z-shaped wing is more effective to improve energy margin and extend perpetual flight days with the same increase of solar cell efficiency. The results can provide valuable engineering reference on optimum wing morphing control and optimum attitude planning for Z-shaped stratospheric solar aircraft.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica, Volume 164〈/p〉 〈p〉Author(s): Chaolong Li, Xiang Zhao, Zhixun Xia, Likun Ma, Binbin Chen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this paper, the influence of vortex generator on the performance of solid scramjet was investigated by means of direct-connected fire tests. The experiments simulated a flight Mach number 5.5 at 23 km. Hydrocarbon fuel was used as the fuel-rich solid propellant. The experimental results show that compared with the benchmark configuration, where no vortex generator was employed, the configurations with vortex generator can promote significantly the ignition and stable combustion of the primary fuel-rich mixture produced in the gas generator. The combustion efficiency of the test no.3 (with a strut) in the supersonic combustor reaches 0.60, while it is only 0.11 in the benchmark test. The vortex generators (ramp or strut) can promote the ignition of the primary fuel-rich mixture and therefore decrease significantly the ignition delay time in the supersonic combustor. And the ignition delay time in the test no.3 (a strut) is shorter than that of in test no.2 (a ramp). In summary, the vortex generators in these experiments play an important role in ignition, and flame stabilization of the fuel-rich mixture in the supersonic combustor of the solid rocket scramjet.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica, Volume 164〈/p〉 〈p〉Author(s): Jian Sun, Jin Zhou, Shijie Liu, Zhiyong Lin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Rotating detonation engines (RDEs) are widely studied because of their compact configurations and high thermal cycle efficiency. In previous literatures, many investigations on the mixing process in an RDE and the rotating detonation wave (RDW) propagation under non-premixed conditions have been published. However, the two issues were investigated separately, and the interaction between the RDW propagation and reactant mixing has not been studied yet. In this paper, a series of three-dimensional numerical simulations of the mixing process and the RDW propagation in an RDE are performed. The transient explicit density-based solver in ANSYS Fluent is used to perform the simulations. In the cold mixing flowfield, as the back pressure at the chamber exit increases, the axial velocity decreases, and the average resident time of reactant in the chamber increases. Thus the fuel has more time to mix with air in the chamber to provide a better mixing quality. The RDW velocity is very stable during the operation time, whose average value is about 1895 m/s. The velocity deficit is very small. After RDW initiation, the pressure in the combustion chamber increases due to the detonation process. The increased pressure slows down the flowing of the reactant, thus the average resident time of reactant within the height of the RDW increases, making the mixing quality better. The enhanced mixing quality of reactant in turn makes the RDW stronger. Thus, there is a positive feedback between RDW propagation and the reactant mixing.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 20 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica〈/p〉 〈p〉Author(s): S.-S. Wei, M.-.T. Lee, Y.-H. Chien, T.-H. Chou, J.-S. Wu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉One of the issues of using a normal graphite nozzle for the hybrid rocket propulsion is the serious throat erosion due to combustion with a higher O/F ratio. This may undermine the throttling capability of the hybrid rocket engine. In this study, we would like to address how the propulsion performance changes under the conditions of different nozzle throat diameters and O/F ratios. We designed and tested a 40-kgf class single-port hybrid rocket motor with the swirling injection of oxidizer, which utilizes the 90 wt% hydrogen peroxide and polypropylene (PP) as oxidizer and fuel, respectively. Three different diameters of graphite nozzle throat (10, 11, and 12 mm) were used to approximate various conditions of nozzle erosion, while the mass flow rates of the injected oxidizer were kept the same. The hot-fire test results indicated that the thrust was nearly the same even the nozzle throat diameters and O/F ratios were different. Especially, the discrepancies among the measured thrusts and oxidizer ISP under various test conditions were found to be less than 1%, which is highly beneficial for the purpose of the thrust control using mass flow rate control of the oxidizer for a hybrid rocket engine with swirling injection of high-concentration hydrogen peroxide.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 21 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica〈/p〉 〈p〉Author(s): Daniel Sagath, Christopher Vasko, Elco van Burg, Christina Giannopapa〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The European Space Agency (ESA) has been the main programmatic and industrial capacities development organisation of the European space sector since its establishment in the early 1970s. Understanding the national policies of its member states is crucial for the future development of a coherent European Space Policy. Over the last years, ESA has developed a methodology to track the development of national space policies of its member states and collaborating states. The “Member States Observatory” is a basic resource for understanding the complexity of the European national space strategies available to the national delegates, ESA experts and employees. The main objective of this study is to present the findings and methodology of two surveys performed in 2013 and 2017, in order to identify the main space strategy developments of the ESA member states. The study suggests two main dimensions, which serve to identify trends in ESA member states. These are space 〈em〉governance structure〈/em〉 and 〈em〉public policy priorities〈/em〉 in technology domains, areas of sustainability, and motivations for engaging in space activities.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica, Volume 164〈/p〉 〈p〉Author(s): Yue Hu, Jianguo Tan, Liang Lv, Xiangdong Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Numerical and experimental studies on 1-D, steady premixed methane-air flames were performed to investigate the quantitative measurement of heat release rate (HRR) using chemiluminescence. A detailed reaction mechanism, incorporating sub-reaction models for excited state radicals (CH* and OH*) was employed in the numerical study. The numerical work utilized the CHEMKIN-PRO package to investigate the distribution rule of excited state radicals and HRR. The heat release characteristic of elementary reactions and the relationship between net reaction rate and HRR were analyzed as well. According to the result of numerical study, experimental work was conducted to measure the HRR and chemiluminescence of OH* and CH* in the flat flames. The distributions of HRR and chemiluminescent intensity were measured by high-accuracy coated Pt/13%-Rh-Pt thermocouple and ICCD camera, respectively. The results shows that OH* and CH* are located in the narrow area where severe chemical reactions occur with much heat release. Compared to CH*, OH* is more effective in marking the spatial distribution of HRR and the correlation between chemiluminescent intensity and HRR possesses characteristic of linearity. Thus, the HRR quantitative measurement method using chemiluminescence has been acquired.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 23 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica〈/p〉 〈p〉Author(s): Xiuqiang Jiang, Shuang Li, Roberto Furfaro〈/p〉

Beschreibung: 〈p〉Publication date: November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica, Volume 164〈/p〉 〈p〉Author(s): Vladimir S. Aslanov〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A new way to removal small space debris using a heavy collector in GEO is considered. The proposed scenario involves three types of consecutive maneuvers: capturing of debris into an area bounded by Hill sphere of the heavy collector, towing and discharging debris in a graveyard orbit. The plane motion equations of the debris relative to the collector are written in the Local-Vertical-Local-Horizontal frame taking into account the engine thrust of the collector. Also considering the engine thrust, the equation motion of the collector in oscillating elements is written. The interaction of the debris and the collector is described by means of the inelastic impact theory. The values of the thrust force of the collector are determined, at which the debris can be captured and towed or discharged in the graveyard orbit. It has been shown numerical simulation, that the proposed maneuvers can be implemented.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 21 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica〈/p〉 〈p〉Author(s): Mo-yao Yu, Ya-zhong Luo〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The path of attitude motion for a rigid body in fully nonlinear Lyapunov periodic orbits is planned in the restricted three-body problem. The attitude dynamic characteristics in phase plane are analyzed, and the path constraint conditions are proposed to avoid the divergence of phase trajectories. Then, the path planning method for the three-body problem is proposed by employing the Pseudospectral method. Based on this, solving strategy of attitude-orbit coupled periodic solutions is obtained by adding event constraint conditions. Compared with previous work, the proposed method effectively avoids the divergence of attitude motion and saves a large amount of work on determining the initial guess. To verify the effectiveness of the proposed method, a large number of planning work are carried out. Besides, the paper addresses the question that how translational motions and configuration of the spacecraft affect the planned results.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 20 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica〈/p〉 〈p〉Author(s): Yuchen She, Shuang Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper investigates the attitude control problem of a two-body combined spacecraft by considering the unilateral contact constraint on the active spacecraft’s end-effector. Previous work has shown that this constraint may cause a relative sliding motion between the end-effector and the target, which has a large impact on the combined spacecraft dynamics and postcapture control process. In this paper, an extra degree-of-freedom approach is adopted and a new dynamical model is developed to efficiently describe the movement of the combined spacecraft in both rigid connecting and relative motion modes. A new control law is also developed to reduce the relative sliding motion between the end-effector and the target while controlling the attitude of the combined system. Simulation results show that the extra degree-of-freedom model proposed in this paper has the correct dynamic properties and that the newly developed controller is a significant improvement over traditional PD controllers in maintaining the geometric configuration of the combined spacecraft.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica, Volume 164〈/p〉 〈p〉Author(s): Amit Padaki, Ashrithpal Police Reddy, Kris Lehnhardt〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In order for astronauts to live and work in outer space, environmental conditions must be maintained within very strict parameters. Any change in these conditions (such as atmospheric composition, pressure, and/or temperature) could pose a risk to the astronauts and ultimately to the success of the mission itself. In particular, changes in pressure could place the astronaut at risk for decompression illness (DCI), a potentially life-threatening condition related to the presence of nitrogen bubbles within the body. There are a number of strategies in human spaceflight designed to minimize the risk of DCI or treat it if necessary. However, as humans prepare again to travel beyond Low Earth Orbit (LEO), the risk of developing DCI may increase, as would the difficulties in treating it, given that evacuation to Earth will become substantially less feasible. Even though hyperbaric oxygen therapy (HBOT) is the accepted gold standard for the treatment of DCI on Earth, there is currently limited capacity for this treatment option in space. Expanding HBOT capacity in human spaceflight could prove useful, given that this medical capability can also be used for the treatment of a number of other potentially life-threatening conditions, such as carbon monoxide poisoning, thermal burns, and gangrene. This paper will examine the current issues related to HBOT in space and discuss the opportunities for its use in future human spaceflight endeavors.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): David Sedmidubský, Vít Jakeš, Kateřina Rubešová, Pavla Nekvindová, Tomáš Hlásek, Roman Yatskiv, Pavel Novák〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Using the recently developed method based on a combination of DFT plane wave code applied to extract the crystal field parameters and a local atomic like Hamiltonian involving electron-electron, spin-orbit and Zeeman terms we calculated the energy levels of ground and excited multiplets of Yb〈sup〉3+〈/sup〉 and Er〈sup〉3+〈/sup〉 ions hosted in ytterbium and yttrium aluminum garnet (YbAG and YAG) including their crystal and magnetic field splitting. The obtained energy levels and derived magnetic properties are compared with the experimental data from magnetometry, photoluminiscence and near-infrared spectroscopy.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925838819331421-fx1.jpg" width="242" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 30 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 811〈/p〉 〈p〉Author(s): Yan Jia, Si'an Chen, Yong Li, Song Wang, Haifeng Hu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉C/C–ZrC–SiC–ZrB〈sub〉2〈/sub〉 composites were prepared by a joint process of precursor infiltration and pyrolysis and slurry infiltration. The high-temperature mechanical properties of the composites were reported and the evolution of fracture behavior and microstructure was analyzed. The composites exhibited a tensile strength and flexural strength of 99.3 MPa and 281 MPa, respectively during the test at ambient temperature. The high temperature in-situ tensile properties were higher than those at ambient temperature; the tensile strength was 136 MPa during the tensile test at 1700 °C. This is because the energy absorption mechanisms will occurred during the high-temperature test. The high temperature in-situ flexural strength was 223 MPa during flexural test at 1800 °C. However, the flexural strength of as-prepared composites after heat treat at 1800 °C was maintained at 153 MPa, which was lower than that of the in-situ flexural test at 1800 °C, because the fibers were more seriously eroded after heat treatment at 1800 °C. After heat treatment at 2400 °C, the flexural strength of the composites decreased to 88 MPa. It can be inferred that the high temperature in-situ flexural strength at 2400 °C was higher than 88 MPa, showing outstanding ultra-high temperature mechanical properties. Therefore, the C/C–ZrC–SiC–ZrB〈sub〉2〈/sub〉 composites are promising to be applied as structural material in aerospace, due to their excellent high-temperature mechanial properties at 1500 °C–2400 °C.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): Qi Li, Liguo Yue, Li Li, Hui Liu, Wenqin Yao, Ning Wu, Longwen Zhang, Hao Guo, Wu Yang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Nitrogen sulfur co-doped bimetal nanocomposites (NS-BNs) are prepared through vulcanization and annealing using bimetallic Ni/Co-MOF as a precursor. The nitrogen sulfur co-doped bimetal nanocomposites have abundant electroactive sites and redox reaction centres, which exhibit remarkable electrochemical performance as electrode materials for supercapacitor. The specific capacitance could reach 1529 F g〈sup〉−1〈/sup〉 at a current density of 1 A g〈sup〉−1〈/sup〉 and excellent cycle stability (retention rate of 89.29% after 10000 cycles). After the current density is expanded ten times, the specific capacitance can still reach 1069 F g〈sup〉−1〈/sup〉, indicating superior rate performance. Furthermore, the assembled asymmetric supercapacitor displayed a high energy density of 41.04 Wh kg〈sup〉−1〈/sup〉 at power density of 750 W kg〈sup〉−1〈/sup〉. As a result, non-metal doped nanocomposites material has promised applications for electrochemical supercapacitors.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925838819332074-fx1.jpg" width="346" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): Yun Wei, Yupeng Shi, Zhiyang Jiang, Xuefeng Zhang, Huihui Chen, Yahong Zhang, Jingwei Zhang, Chunhong Gong〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this study, titanium nitride (TiN)/reduced graphene oxide (RGO) composites were prepared via a facile hydrothermal and thermal nitridation process. Due to their favorable electromagnetic wave dissipation ability and appropriate electromagnetic (EM) impedance matching, the TiN/RGO flakes embodies distinct advantage as compared to single component RGO nanosheets and TiN nanoparticles. Moreover, the effective electromagnetic absorption frequency range of the TiN/RGO flakes could be designed by controlling the mass ratio of the precursor. When the mass ratio of nanosized titanic acid to graphene oxide is 1.4:1, the reflection loss of the TiN/RGO with only 2.0 wt% absorber loading reaches −42.85 dB at 8.88 GHz with a thickness of 4.0 mm and a broad effective absorption bandwidth (〈em〉R〈/em〉L 〈 −10 dB) of 6.7 GHz, which compete well with those observed in several RGO-based composites with much higher filler loadings. The combined excellent EM absorption property with simple production procedure and ultralow absorbent content requirement endow the TiN/RGO flakes as a promising lightweight and efficient EM absorption material suitable for harsh application conditions.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 25 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 810〈/p〉 〈p〉Author(s): X.H. Shi, C. Zhao, Z.H. Cao, Z.H. Wang, R.P. Guo, J.W. Qiao, Y.C. Wu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The yielding, deformation and fracture behavior for the Widmanstätten structure of Ti–8Al–1Mo–1V alloy upon high speed impact were studied through characterization and discussion. Seven strain rates ranging from 870 s〈sup〉−1〈/sup〉 to 3300 s〈sup〉−1〈/sup〉 were applied. The results show that: The yield strength of Widmanstätten structure shows two distinct changing stages among the whole range of strain rates. Under the strain rates below 2250 s〈sup〉−1〈/sup〉, Widmanstätten structure exhibits positive strain rate sensitivity. Surprisingly, under the strain rates from 2250 s〈sup〉−1〈/sup〉 to 3300 s〈sup〉−1〈/sup〉, it shows negative strain rate sensitivity. The increasing importance of twinning in the initiation of plastic deformation with higher strain rate is deemed as the reason causing this phenomenon. The dynamic compression behavior of Widmanstätten structure is described by J-C model, which shows unstable prediction performance. Adiabatic shearing band starts forming under the strain rates above 1950 s〈sup〉−1〈/sup〉, from which the fracture behavior of Widmanstätten structure is analyzed. An interesting phenomenon is that the adiabatic shearing band thicknesses at different locations of specimen can be obviously different. This is attributed to the relative orientation of α lamellae to the biggest shear stress plane. Saw-tooth chips start forming at the two end faces of specimen under the strain rates above 2500 s〈sup〉−1〈/sup〉, and its formation mechanism is thoroughly discussed. Adiabatic shearing band after post annealing was characterized by EBSD, which shows recrystallized grains with gradient diameters. In addition, it is found that the Burgers orientation relationship of the microstructure outside adiabatic shearing band was generally retained during the dynamic loading and post-annealing process.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica, Volume 164〈/p〉 〈p〉Author(s): Qiang Liu, Zhenbing Luo, Xiong Deng, Dengpan Wang, Lin Wang, Yan Zhou, Pan Cheng〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The interaction between self-sustaining dual jets and supersonic laminar boundary layer is experimentally studied using the nanoparticle-based planar laser scattering in a Ma 2.95 supersonic low-turbulence wind tunnel for the first time. The typical fine flow structures, such as separation shock, “W” bow shock, barrel shock, horseshoe vortex, large-scale vortex structures and counter-rotating vortex pairs, are clearly identified by streamwise and spanwise flowfield images. The curves of jet penetration depth are fitted at the momentum ratio of 0.55 between self-sustaining dual jets and supersonic crossflow. The results play a significant role in further and comprehensive exploration of the active flow control for a supersonic flow.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica, Volume 164〈/p〉 〈p〉Author(s): Sophie Gruber, Gernot Grömer, Olivia Haider〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Austrian Space Forum in cooperation with the Oman Astronomical Society conducted a high-fidelity Mars Analog field simulation in the Dhofar region, Sultanate of Oman in February 2018. Directed by a Mission Support Center in Austria, a carefully selected and trained field crew of 15 researchers conducted experiments from various disciplines (e.g. engineering, planetary surface operations, astrobiology, geophysics/geology, life sciences) preparing for future human Mars missions. Mars analog research in a representative environment is also an excellent tool to enhance the visibility of planetary sciences and to engage with the next generation of researchers. To reach out to young students from 6 to 25 years, special programs and initiatives were set-up. This paper focuses on the Junior Researchers Program, where four high school and undergraduate student teams realized their experiments in a scientific mission, starting with defining their research questions, building their experiment hardware and finally analyzing and publishing the outcomes.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica, Volume 164〈/p〉 〈p〉Author(s): Gao Yonggang, Liu Yang, Chai Zexin, Li Xiaocong, Hu Chunbo, Yu Xiaojing〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The highly efficient and organized combustion of combustors should be achieved to improve the performance of solid fuel rocket scramjets. This study investigated the influence of changes in lobe sweep angle and height on the mixing and heat release characteristics of a solid fuel scramjet combustor on the basis of a staggered support plate structure introduced in a previous experimental study. The goal was to determine the optimal parameters of lobe sweep angle and height for subsequent engine design. Numerical simulation was conducted to quantitatively analyze the mixing and heat release characteristics of the combustor at different lobe sweep angles and heights in terms of combustion efficiency, gas mixing degree, and oxygen–fuel ratio. Results demonstrate that 1) the lobe sweep angle should be based on the width and straight section length of the staggered support plate structure. Engine performance improves with the decrease of the lobe sweep angle. 2) There is an optimum lobe height in the range of 0–24 mm, and the optimum value point is approximately 14 mm according to the proposed engine configuration.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 21 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica〈/p〉 〈p〉Author(s): Guanlin Fang, Zhijun Wei, Zhiwen Wu, Rui Du, Ningfei Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This study proposes an embedded rocket ramjet, a novel combined ramjet engine, that can operate at high altitude and low pressure. The embedded rocket ramjet combustor is investigated experimentally and numerically to predict its characteristics. Experiments are performed in a direct-connect ground test facility to measures the wall pressure and total pressure at the combustor exit. Three-dimensional Navier–Stokes equations and species transport equations are solved numerically. A compressible reactive shear stress transport k-ω turbulence model with reduced chemical kinetics of a surrogate model for kerosene is used to study the flow characteristics and overall performance of the combustor. Test results show that the embedded rocket can significantly increase the combustor pressure. Numerical analysis shows that the embedded rocket increases the mixing efficiency, combustion efficiency, and thrust but decreases the specific impulse.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica, Volume 164〈/p〉 〈p〉Author(s): Federica Angeletti, Paolo Gasbarri, Marco Sabatini〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Large deployable antennas are required for the advancement of space communications, Earth observation, radio astronomy and deep space exploration. Most contemporary space antennas have exceeded the size of launching vehicles, leading to the necessity of stowed concepts to overcome the limitation. Many structural models have been investigated by different organizations. Generally, mesh deployable reflectors are currently more mature compared to other foldable solutions. This will be the topic of this paper. Orbital disturbances, perturbations originated by on-board sources and thermal deformations affecting the deployed configuration can deteriorate the accuracy of the communications system. Undesired dynamic behaviour of structural components has to be predicted and counteracted. Therefore, vibration control is a key technology to correct the distortions altering the proper functioning of the system. An intelligent active structure is introduced as a structure configured with distributed actuators and sensors and guided by a controller to modify the dynamic response of the system. In this paper, the supporting structure of a very large mesh reflector is described. A FEM formulation is adopted to assemble the frame and it is validated by comparing it with commercial codes. According to the adopted model, the active elements can be embedded in the middle of the truss elements. Of course, active control of all the devices at the same time requires a control effort which could be not affordable in space applications. However, the effectiveness is not the same for all the actuators. In this study, two cascade optimization procedures are performed to assess the best positioning and velocity feedback gains of the actuators that must be controlled to damp vibrations. In particular, a gradient-based technique is used after both a Genetic Algorithm and a Reinforcement Learning methodology to find the best set of gains for the controller. The objective function is set as a weighted sum of power consumption of the actuators. As a study case, the spacecraft implements a velocity feedback strategy when performing a generic attitude manoeuvre to coordinate the simultaneous action of the devices to ensure the damping performance of the system is enhanced. In addition, the impact of damaged actuators and uncertainties on the mechanical properties of the passive structure has been discussed and analysed.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica, Volume 164〈/p〉 〈p〉Author(s): James C. Beck, Ian Holbrough, Thorn Schleutker, Ali Guelhan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The assessment of casualty risk in destructive re-entry has historically been performed purely by simulation using heating correlations, which only have verification on basic shapes, and estimated phenomenology for fragmentation. As the application of space debris mitigation requirements is expected to result in a higher number of re-entries, this has brought a stricter enforcement of the casualty risk guidelines to proposed missions. In turn, this has increased the interest in designing spacecraft to demise in re-entry in order to allow uncontrolled re-entries to be performed. Initial testing of spacecraft materials and basic structures has demonstrated that the destructive re-entry tools do not capture the correct physics to be able to assist design in a meaningful way, and therefore, some means to improve the representativeness of the tools is required. The current understanding of the phenomenology of the fragmentation and demise processes is limited. As a consequence, it is vital to perform appropriate tests in order to improve the capability of the tools to assist the design process. To this end, a set of destructive tests on spacecraft materials, structures and components has been performed in an arc-heated supersonic wind tunnel. These tests include the first destructive wind tunnel tests ever performed on a complete nano-satellite and a reaction wheel. From these tests, it has been determined that the failure of aluminium structures is highly dependent upon the behaviour of the protective metal oxide layer, and that this can be catastrophic in nature. The tests on the nano-satellite have shown that the structure can be supported by stainless steel spacers between the electronics cards, and that glass fibre reinforced plastic PCBs are more resistant to melting than had been anticipated. The reaction wheel test has shown that the connections between parts are critical to the fragmentation and demise processes, as the glued housing separates quickly, well before melt temperature is reached at the joint. It has also demonstrated the importance of radiative cooling, as the flywheel and ball-bearing unit have survived a test at over 800 kW/m〈sup〉2〈/sup〉 with little damage.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 20 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica〈/p〉 〈p〉Author(s): Xin Chen, Jiancheng Yang, Dandan Dong, Huanhuan Lv, Bin Zhao, Yanru Xue, Peng Shang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Exposure to microgravity during long-term habitation in space results in numerous physiological alterations in the human body. Among them, reduction in bone mineral density is well known as one of the most important changes, which limits further space exploration by humans. Although numerous studies have been conducted on microgravity-induced bone loss, the explicit mechanism behind its occurrence has not been fully elucidated. Even though mechanical unloading has been generally accepted as a dominant cause of microgravity-induced bone loss, the risks of iron-loading and oxidative damage due to increased iron stores and dietary iron intake during spaceflight have attracted much attention, especially in bone. Indeed, excessive iron accumulation has been found in astronauts exposed to microgravity during spaceflight. Moreover, a great deal of evidence from clinical, animal, and cellular studies indicates that iron-loading has direct adverse effects on bone metabolism. This review summarizes the latest findings on bone loss and iron status in microgravity conditions, as well as the association between iron-loading and bone abnormalities. We discuss the possible mechanisms of iron overload-induced skeletal involution. Finally, we hypothesize that, in addition to mechanical unloading, iron overload due to long-term spaceflight missions is a high risk factor for microgravity-induced bone loss. The underlying mechanism by which it occurs is iron-loading that leads to an imbalance in bone remodeling, involving bone formation and bone resorption, mediated by oxidative stress via the Fenton reaction.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Astronautica, Volume 164〈/p〉 〈p〉Author(s): Shuji Yang, Hao Wen, Dongping Jin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper presents a trajectory planning method for a dual-arm space robot that is free-floating and receives no actuation from the base spacecraft. The task is to capture a target by a mission arm and accomplish base manoeuvring with the coupling effects by a manoeuvring arm. Three manoeuvring cases for the base are discussed concerning attitude regulation, attitude tracking and position tracking. In all cases, an optimization method is applied to solve for the joint velocity of the arms, which ensures that the joint states of the mission arm obtain the desired states for capturing and control the motion of the base. Moreover, the collision avoidance of the manoeuvring arm with the base and mission arm is considered an inequality constraint. In particular, the joint velocity of the mission arm is represented by a new variable to remove the disturbance caused by the mission arm on the attitude of the base which makes it easier to complete the attitude manoeuvring case. Finally, numerical simulations are carried out by the planar and spatial dual-arm robots to validate the efficiency of the control strategy during both capturing and base manoeuvring.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: 25 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Alloys and Compounds, Volume 806〈/p〉 〈p〉Author(s): Krishna K. Pawar, Jasmin S. Shaikh, Sawanta S. Mali, Yuvraj H. Navale, Vikas B. Patil, Chang K. Hong, Pramod S. Patil〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Herein, we report a facile approach for the synthesis of hollow Indium oxide (In〈sub〉2〈/sub〉O〈sub〉3〈/sub〉) microcubes (HIMC) by two step process which consist of hydrothermal method and followed by air annealing. Kirkendall effect has been employed to transform Indium hydroxide In(OH)〈sub〉3〈/sub〉 microcubes (IHMC) to HIMCs. Particularly, the formation of HIMC was studied as function of annealing time. The evolution of hollowness was discussed through Kirkendall effect. Fabricated HIMC films were used to detect NO〈sub〉2〈/sub〉 gas up to 100 ppm of concentration. We found that synthesized HIMC had a huge sensing response (S = 1401) towards 100 ppm NO〈sub〉2〈/sub〉 gas, which demonstrates the effect of HIMC over simple microcubes. Response (R〈sub〉s〈/sub〉 = 16s) and recovery (R〈sub〉c〈/sub〉 = 165s) time of sensor were very short, which enables sensor to work rapidly. Also, HIMC sensor found selective for NO〈sub〉2〈/sub〉 gas rather ammonia, acetone and carbon dioxide gases. NO〈sub〉2〈/sub〉 sensing mechanism for the case of HIMC based sensor was described as per well known oxide based chemiresistive theory. From observations, it is found that the fabricated (HIMC)〈sub〉3hr〈/sub〉 based sensor is highly selective and sensitive towards NO〈sub〉2〈/sub〉 gas at ppm level of concentration and could be undertaken for gas sensing application at various fields.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S092583881932763X-fx1.jpg" width="240" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉